UC-NRLF 


B  ^  as7  DD3 


GIFT   OF 


ROBISON'S  MANUAL 

OF 

RADIO   TELEGRAPHY 

AND 

TELEPHONY 

1918 


ROBISON'S  MANUAL 


OF 


RADIO  TELEGRAPHY 


AND 


TELEPHONY 


FOR  THE  USE  OF 


NAVAL  ELECTRICIANS 


BY 
CAPTAIN  S.  S.  ROBISON,  U.  S.  NAVY 


REVISED  BY 

CAPTAIN  D.  W.  TODD,  U.  S.  NAVY 
Director  Naval  Communications 

AND 

LIEUT.  COMMANDER  S.  C.  HOOPER,  U.  S.  NAVY 
In  Charge  of  Radio  Division,  Bureau  of  Steam  Engineering 


4th  revised  EDITION 


ANNAPOLIS,   MD. 

THE  UNITED   STATES  NAVAL  INSTITUTE 

1918 


ROBISON'S  MANUAL 

OF  RADIO  TELEGRAPHY  AND  TELEPHONY 

Price,  $1.50,  postpaid 


Copyright,  1911 

BY 

PHILIP  R.   ALGER 

Secretary  and  Treasurer,  U.  S.  Naval  Institute 


Copyright,  1912 

BY 

RALPH  EARLE 

Secretary  and  Treasurer,  U.  S.  Naval  Institute 


Copyright,   1913 

by 

E.  J.  KING 

Secretary  and  Treasurer,  U.  S.  Naval  Institute 


oitt 


Copyright,  1918 

BY 

J.  W.  CONROY 

Trustee  for  U.  S.  Naval  Institute 
Annapolis,  Md. 


c 


Z2)t  £orb  (^aftmore  (pr«»g 

BALTIMORE,   MD.,  U.  S.   A. 


PREFACE 

This  manual,  first  published  in  January,  1907,  was  revised  in  1909  by 
L.  W.  Austin,  Ph.  D.  The  present  (2d)  revision  contains  the  results  of 
some  of  Dr.  Austin's  later  researches  as  well  as  more  detailed  instructions 
relative  to  installation,  care  and  operation,  also  additional  appendices, 
containing  extracts  from  Service  Eegulations  adopted  at  the  International 
Wireless  Telegraph  Convention  in  Berlin,  October,  1906,  and  the  U.  S. 
Statute  of  1910,  relative  to  wireless  telegraph  apparatus  on  merchant 
vessels. 

The  author  is  also  indebted  to  Mr.  J.  Martin,  of  the  Navy  Yard,  New 
York;  Mr.  Geo.  F.  Hanscom,  of  the  Navy  Yard,  Mare  Island;  Mr.  Geo. 
H.  Clark  and  others  for  figures,  illustrations  and  suggestions. 

July,  1911. 


PREFACE  TO  THIRD  REVISION 

Advantage  has  been  taken  of  the  necessity  for  a  new  edition  to  regroup 
subjects;  to  add  articles  and  figures  relating  chiefly  to  the  use  of  un- 
damped oscillations;  to  note  the  results  of  some  of  Dr.  Austin's  recent  re- 
searches; to  alter  appendices  to  include  the  London  Convention  of  1912 
and  the  U.  S.  Statute  of  1912,  and,  through  the  kindness  of  Lieutenant 
S.  C.  Hooper,  U.  S.  N.,  to  extend  the  chapter  on  care  and  operation. 

August,  191S. 


A  new  edition  being  necessary,  minor  corrections  and  additions  to  the 
third  revision  have  been  made. 
December,  19H. 


PREFACE  TO  FOURTH   REVISION 

The  copies  of  previous  editions  having  become  exhausted,  certain 
changes  have  become  necessary  to  bring  the  Manual  up-to-date.  Owing 
to  the  many  responsibilities  placed  upon  Captain  Eobison,  due  to  the 
war,  the  revision  has  been  made  by  Captain  Todd  and  Lieutenant  Com- 
mander Hooper,  who  offer  the  Fourth  Edition  as  Eobison's  Manual  of 
Radio  Telegraphy  and  Telephony.  Credit  is  due  to  Lieutenant  H.  P. 
LeClair,  U.  S.  Navy,  in  charge  of  the  Eadio  Division,  Bureau  of  Steam 
Engineering,  and  Mr.  Charles  J.  Pannill,  Expert  Eadio  Aide,  Office  of 
Director  Naval  Communications,  for  many  valuable  suggestions  and  their 
work  in  connection  with  the  revision  of  this  Manual. 

January,  1918. 


it) 


CONTENTS 


CHAPTER  I. 

General  Review  of  Facts  Relating  to  High-Frequency  Currents. 

Electricity;  Magnetism;  Electro-magnetism;  Electro-magnetic  induction; 
Relation  of  positive  direction  of  lines  of  force  to  positive  direction  of  current; 
Methods  of  producing  currents  by  electro-magnetic  induction;  Production  of 
electric  and  magnetic  fields  stresses  and  strains  in  the  ether;  Electric  capacity; 
Electric  and  magnetic  induction;  Electric  condensers;  Discharge  of  con- 
densers; Ether  waves;  Reflection  of  ether  waves;  Refraction;  Diffraction. 

CHAPTER  II. 
Production,  Radiation   and  Detection  of  Ether  Waves. 

Mutual  induction  and  coupling;  Transfer  of  energy  between  coupled 
circuits;  The  quenched  gap;  Methods  of  producing  electric  waves;  Radiation 
of  electric  waves;  Damped  oscillations;  Undamped  oscillations;  Decrease  of 
amplitude  with  distance  from  source;  Detection  of  electric  waves;  Receiving 
circuits. 

CHAPTER  III. 
Electric  Units  and  Their  Relations  to  Each  Other. 
Volt;  Ampere;  Ohm;  Watt;  Coulomb;  Farad;  Henry. 

CHAPTER  IV. 

Capacity  and  Self-Induction. 

Fundamental  Equation  of  Wireless  Telegraphy;  Self-induction;  Capacity; 
Condensers  and  Inductances  in  series  and  in  parallel;  Combination  of  self- 
induction  and  capacity  in  oscillating  circuits;  Capacity  and  self-induction 
of  straight  wires;  Time  constants  of  condensers  and  inductive  circuits; 
Difference  between  D.  C.  and  A.  C.  due  to  self-inductance  and  capacity; 
Skin  effect  of  high  frequency  A.  C. ;  Measurements  of  inductance  and  capacity 
in  oscillating  circuits. 

CHAPTER  V. 

Power  ExrENniTURE  and  Efficiency  of  Sending  and  Receiving  Apparatus. 

Mechanical  work  done  in  making  dots  and  dashes  of  the  telegraph  code; 
Efficiency  of  sending  apparatus;  Losses  in  condensers;  Losses  in  closed  and 
opened  circuits;  Relations  between  height  of  aerial,  Oscillating  current.  Wave 
length  and  distance  of  transmission;  Efficiency  of  receiving  apparatus; 
Increase  of  efficiency  due  to  a  high  spark  frequency;  Comparison  of  efficiency 
using  damped  and  undamped  waves;  Losses  in  receiving  circuits. 


8     .     ,  r     -    ■  CONTENTS. 

CHAPTER   VI. 

Sending  Apparatus. 

Generators;  Considerations  governing  frequency  of  generators;  Trans- 
formers; Regulation  of  A.  C.  sending  apparatus;  Sending  keys;  Closed 
circuits  (inductance,  condenser,  spark  gap);  Condensers;  Dielectric  strength 
of  air;  Spark  gaps;  Use  of  the  arc  for  producing  undamped  oscillations;  The 
Federal-Poulsen  System  of  Radio  Telegraphy;  The  antenna;  The  ground; 
The  helix;  Wave-changing  switches,  etc.;  Signals  and  Keys;  The  arc; 
Receiving;  Wireless  Telephone  transmitters;  Limitations  on  wave  lengths; 
Open  circuit  (Aerial,  inductance,  ground);  Open  circuit  inductance;  Aerial 
accessories;  Grounds  and  ground  connections. 

CHAPTER  VII. 

Receiving  Apparatus. 

Navy  receiving  sets  type  A;  Variable  condensers;  Condensers  in  receiving 
circuit;  Inductances  in  receiving  circuit;  Detectors;  Electrolytic  detectors; 
Rectifying  detectors;  Vacuum  tube  detectors;  The  oscillating  audion;  Mag- 
netic detector;  Slipping  contact  detector;  Coherers  and  Lodge-Muirhead 
detector;  Testing  buzzers;  Receiving  telephones;  Relays  or  ampliphones; 
Recording  apparatus;  Direction  finders;  Belini-Tosi  wireless  compass;  Port- 
able and  auxiliary  sets;  Airplane  radio  transmitter. 

CHAPTER  VIII. 
Installations,  Adjustments  and  Measurements. 
Installations;  Protective  devices;  Adjustments;  Measurements,  wave  meters 
and  their  use;  Measurements  of  wave  lengths;  Instructions  for  using  the 
Pierce  wave  meter  of  the  Massachusetts  Wireless  Equipment  Company;  (a) 
Calibration  of  sending  station;  (b)  Calibration  of  receiving  station;  (c) 
Precaution  and  care  of  the  instrument;  Tuning  curves;  Resonance  and  audi- 
bility curve;  Measurement  of  damping;  Measurement  of  sending  current;  The 
shunted  telephone  method  of  measuring  the  intensity  (loudness)  of  signals; 
Measurement  of  inductance  and  capacity  and  total  resistance;  The  measure- 
ment of  logarithmic  decrement. 

CHAPTER  IX. 

Care  and  Operation. 

Calling;  Sending;  Duplex  operation;  High-speed  operation;  To  send  a 
message;  Receiving;  Interference;  Static;  Codes;  International  Morse  code 
signals;  Abbreviations;  Commercial  operation  by  United  States  Naval  Com- 
munication Service;  Sources  of  information. 

APPENDICES. 


ROBISON'S  MANUAL 

OF 

RADIO  TELEGRAPHY  AND  TELEPHONY 


Chapter  L 

GENERAL  REVIEW  OF  FACTS  RELATING  TO  HIGH 
.   FREQUENCY  CURRENTS. 

ELECTRICITY. 

1.  If  amber  is  rubbed  with  silk  a  change  in  the  condition  of  the  amber 
and  of  the  silk  is  produced  which  can  be  detected  in  various  ways. 

This  change  in  condition  is  described  by  saying  that  the  amber  and 
the  silk  are  electrified  or  charged  with  electricity  by  friction.  Both  of 
these  terms  are  derived  from  the  Greek  word  "  elektron,"  meaning  amber. 

The  silk  and  amber  thus  electrified  attract  each  other  and  bodies  in 
their  vicinity,  but  the  silk  will  repel  another  piece  of  silk  similarly 
electrified  and  the  amber  will  repel  another  piece  of  amber  similarly 
electrified.  Since  amber  and  silk  have  no  effect  on  each  other  when  not 
electrified,  the  qualities  of  attraction  and  repulsion  are  said  to  reside  in 
the  electric  charges,  and  the  fact  is  expressed  by  the  statement  that  like 
charges  repel,  unlike  charges  attract  each  other.  The  silk  is  said  to  be 
positively,  the  amber  negatively,  electrified  or  charged.  Positive  and 
negative  charges  are  indicated  by  plus  ( + )  and  minus  ( — )  signs. 

The  charges  are  said  to  consist  of  static  or  frictional  electricity. 

Bodies  thus  charged  when  not  brought  into  contact  with  each  other 
or  with  what  are  called  conductors  remain  in  an  electrified  condition  for 
some  time. 

Bringing  oppositely  charged  bodies  in  contact  generally  removes  all 
evidences  of  electrification.  The  charges  are  said  to  unite  and,  being  of 
opposite  signs,  to  neutralize  each  other,  and  the  bodies  are  said  to  be 
discharged. 

Sparks  accompanied  by  a  sharp  crackling  sound  are  produced  between 
highly  electrified  bodies  when  brought  very  near  each  other.  After  the 
spark  has  passed  the  bodies  are  found  to  be  discharged. 

Charged  bodies  which  can  be  discharged  by  sparking  at  greater  dis- 
tances than  others  are  said  to  be  charged  to  a  higher  potential. 

All  bodies,  whatever  their  nature,  are  capable  of  being  electrified. 

The  presence  of  static  charges  of  electricity  can  be  shown  by  what 
are  called  electroscopes.    One  of  the  most  sensitive,  the  gold-leaf  electro- 


10 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


scope,  consists  of  two  small  pieces  of  gold  leaf,  which,  becoming  charged 
in  the  same  sense  (i.  e.,  positively  or  negatively),  by  touching  a  charged 
body,  repel  each  other,  and  diverge,  and  show  by  their  divergence  the 
presence  of  electric  charges. 

2.  Certain  bodies,  notably  metals,  have  the  quality  of  transmitting  or 
carrying  electric  charges  through  themselves  and  are  called  conductors. 
Bodies  lacking  in  this  quality,  or  possessing  it  to  a  very  limited  degree, 
are  called  nonconductors,  or  insulators,  or  dielectrics,  according  to  the 
purpose  for  which  they  are  used. 

3.  When  pieces  of  zinc  and  carbon  are  immersed  in  a  conducting 
liquid  (fig,  1)  the  combination  is  called  a  prima/ry  cell.  If  a  wire  is 
connected  to  the  zinc  and  one  to  the  carbon  and  the  free  ends  of  the 
two  wires  brought  near  each  other,  these  ends  are  found  to  be  electrified ; 
the  end  of  the  wire  connected  to  the  carbon  electrified  like  the  silk  (  + ) 
and  the  end  of  that  connected  to  the  zinc  like  the  amber  (  — ).  The 
carbon  is  called  the  negative  element  or  positive  pole  of  the  cell  and  the 


FiQ,  1. 


Fig.  2. 


zinc  the  positive  element  or  negative  pole.  A  number  of  cells  together  is 
called  a  battery.  The  liquid  in  which  the  elements  are  immersed  is  called 
the  battery  solution.  If  the  free  ends  of  the  wires  are  brought  together 
an  electric  current  is  established,  of  which  the  positive  direction  is  said 
to  be  from  the  carbon  to  the  zinc,  through  the  wires ;  from  the  zinc  to  the 
carbon,  through  the  liquid.     (See  fig.  2,  and  note  1,  appendix.) 

The  current  is  said  to  be  caused  by  a  difference  of  potential  between 
the  carbon  and  the  zinc.  It  is  supposed  to  be  made  up  of  small  electric 
charges  transmitted  through  the  wire  in  quick  succession,  the  charges 
being  produced  by  chemical  or  electric  action  between  the  carbon  and 
the  zinc  in  the  liquid. 

The  force  which  causes  the  movement  of  the  electric  charges  which 
make  up  the  current  is  called  the  electro-motive  force  and  is  usually 
written  E.  M.  F. 

If  the  free  ends  of  the  wire  in  fig.  2  instead  of  being  directly  con- 
nected are  immersed  in  another  conducting  liquid,  as  in  fig.  3,  the  cur- 
rent will  flow  through  this  liquid.  The  immersed  ends  are  called 
electrodes.  The  one  at  which  the  current  enters  is  called  the  positive 
and  the  one  at  which  it  emerges  the  negative  electrode.    These  are  also 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


11 


called  the  anode  and  the  catliode,  respectively.     The  conducting  liquid 
in  this  cell  is  called  the  electrolyte. 

4.  If  the  anode  and  cathode  in  fig,  3  are  made  of  lead  (or  prepara- 
tions of  lead)  plates,  and  the  electrolyte  is  a  solution  of  sulphuric  acid 
in  water,  the  combination  is  called  a  secondary  or  storage  cell  or  accumvr 
lator  and  a  number  of  such  cells  is  called  a  storage   battery.      The 


Fig.  3. 


Fig.  4. 


anode  is  called  the  positive  plate  and  the  cathode  the  negative  plate.  If, 
after  a  current  has  been  forced  through  such  a  cell  for  a  time,  the  wires 
from  the  primary  cells  are  disconnected  and  the  positive  and  negative 
plates  connected  by  a  wire  (fig.  4)  outside  of  the  electrolyte,  a  current 
will  flow,  the  positive  direction  of  which  will  be  from  the  positive  to 
the  negative  plate  in  the  wire,  and  from  the  negative  to  the  positive 
plate  in  the  electrolyte. 

5.  For  convenience,  a  battery  of  primary  or  secondary  (storage)  cells 
is  indicated  as  in  fig.  5,  the  elements  forming  positive  poles  by  the  light 


r'^ 


1-.  +i 


Fig.  5. — Cells  in  Series. 


Fig.  5a. — Cells  in  Parallel, 


lines  and  the  elements  forming  negative  poles  by  the  shorter,  heavy  lines. 
Cells  connected  as  in  fig.  5  are  said  to  be  in  series;  connected  as  in  fig. 
5a,  in  parallel. 

MAGNETISM. 

6.  A  magnet  situated  at  a  distance  from  other  magnets  and  pivoted 
80  that  it  is  free  to  move,  will  point  toward  the  north  magnetic  pole  of 
the  earth,  which  in  some  localities  coincides  with  the  north  star  in 


13 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


direction.  That  end  of  the  magnet  wliich  points  in  the  direction  of  the 
north  star  is  called  the  north-seeking  pole,  or  simply  the  north  pole  of  the 
magnet.    The  other  end  is  called  the  south  pole. 

Similar  magnetic  poles,  like  similarly  charged  bodies,  repel  each  other. 
Dissimilar  magnetic  poles,  like  oppositely  charged  bodies,  attract  each 
other — i.  e.,  two  north  poles  or  two  south  poles  repel  each  other:  a  north 
and  a  south  pole  attract  each  other.  The  north  pole  is  sometimes  called 
the  positive  pole  and  the  south  pole  the  negative  pole  of  the  magnet. 

Wrought  or  soft  iron  can  be  magnetized  but  only  retains  its  magnet- 
ism while  under  the  influence  of  the  magnetizing  force;  steel  or  hard 
iron  once  magnetized  retains  its  magnetization  permanently,  and  special 
means  to  demagnetize  it  are  required. 

All  bodies  can  be  electrified,  but  all  bodies  can  not  be  magnetized. 

7.  If  a  sheet  of  paper  is  held  over  a  powerful  magnet  and  iron  filings 
sprinkled  on  the  sheet,  the  filings  will  assume  positions  approximately 


Fig.   6. 


Fig.   7. 


as  sliown  in  fig.  6.  Some  force  connected  with  the  magnet  must  make 
the  filings  assume  these  positions,  which  are  different  from  what  they 
would  be  if  the  magnet  was  not  under  the  paper;  and  from  the  way  the 
filings  are  arranged,  this  force  must  act  in  the  space  surrounding  the 
magnet.  This  space  is  called  the  field  of  magnetic  force,  or  simply  the 
field  of  force,  and  the  lines  in  which  the  filings  tend  to  arrange  them- 
selves are  called  the  lines  of  force,  and  we  shall  see  in  chapter  II  that  this 
conception  is  used  as  a  basis  for  electric  measurements.  The  direction  of 
the  lines  of  force  at  any  point  indicates  the  direction  of  the  magnetic 
force  at  that  point,  and  their  number  in  any  area,  the  strength  of  the 
field  in  that  area. 

It  is  found  that  a  small  magnetic  needle,  pivoted  so  that  it  is  free  to 
move  and  brought  near  the  large  magnet,  will  lie  parallel  to  the  direetion 
of  the  lines  of  force  at  any  point  at  which  it  may  be  placed  in  the  field, 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


13 


and  that  the  north  pole  of  the  needle  always  points  along  the  lines  of 
force  in  the  direction  leading  to  the  south  pole  of  the  magnet. 

The  direction  in  which  the  north  pole  of  the  needle  points  is  called 
the  positive  direction  of  the  lines  of  magnetic  force,  and  the  direction 
in  which  the  south  pole  points,  the  negative  direction  of  the  lines  of 
magnetic  force. 

Lines  of  magnetic  force  are  said  to  run  from  the  north  pole  of  the 
magnet  to  the  south  pole  through  the  air,  and  back  to  the  north  pole 
through  the  steel  (fig.  7). 

ELECTRO-MAGNETISM. 

8.  If  the  wire  in  fig.  1  is  coiled  into  a  spiral,  as  in  fig.  8,  with  the 
positive  direction  of  the  electric  current  as  shown  by  the  arrows  and 


Fig.  8. 


the  battery  connections,  a  field  of  magnetic  force  which  can  be  explored 
by  a  small  magnetic  needle,  or  outlined  by  iron  filings,  as  in  fig.  6, 
will  be  found  to  exist  around  the  spiral,  and  the  direction  of  the  lines  of 
force  will  be  found  the  same  as  those  around  the  magnet  in  fig.  7.  If  the 
current  is  reversed,  the  lines  of  force  are  reversed  in  direction. 

Such  a  spiral,  when  traversed  by  a  current,  is  found  to  have  all  the 
properties  of  a  magnet,  and  is  called  an  electro-magnet  or  solenoid. 

The  strength  of  the  magnetic  field  around  an  electro-magnet  rises 
and  falls  with  the  rise  and  fall  of  the  current,  and  its  polarity  depends 
on  the  direction  of  the  current. 

The  positive  direction  of  the  lines  of  magnetic  force  which  surround 
a  solenoid  is  from  the  north  to  the  south  pole  outside  of  the  spiral,  and 
from  the  south  to  the  north  pole  inside  of  it,  just  as  the  positive  direction 


14  MANUAL    OF    RADIO    TELKGRAPHY    AND   TELEPHONY. 

of  an  electric  current  is  from  the  positive  pole  to  the  negative  pole  out- 
side of  a  battery  and  from  the  negative  to  the  positive  pole  inside  of  it. 

If  the  number  of  turns  of  the  spiral  is  reduced  to  one  it  does  not 
lose  its  magnetic  character.  The  lines  of  force  then  form  circles  around 
the  wire,  tlieir  positive  direction  being  shown  in  fig.  9,  the  upper  side 
being  a  north  pole  and  the  under  side  a  south  pole.  If  the  turn  is 
straightened  out,  as  in  fig.  10,  the  lines  of  force  still  form  circles  around 
the  wire,  and  the  north  pole  of  the  exploring  needle  points  in  the  positive 
direction  of  those  lines.  This  direction  is  found  to  be  always  at  right 
angles  to  the  wire. 

9.  It  appears  from  the  foregoing  that  what  is  called  the  positive 
direction  of  motion  of  electric  currents,  or  charges,  is  related  to  what 
is  called  the  positive  direction  of  the  lines  of  magnetic  force,  in  the 
manner  shown  by  the  arrows  in  figs.  8,  9,  and  10,  and,  further,  that 
the  terms  positive  and  negative  as  applied  to  electric  and  magnetic  effects. 


Fig.  9.  Fio.  10. 

and  so  largely  used  in  connection  with  them,  are  purely  conventional. 
(See  note  2,  appendix.) 

10.  Eeturning  now  to  the  statement  in  article  8  that  the  strength 
of  the  magnetic  field  around  a  solenoid  rises  and  falls  with  the  strength 
of  the  current,  and  its  polarity  (i.  e.,  the  direction  of  the  lines  of  mag- 
netic force  produced)  depends  on  the  direction  of  the  current^  it  can  be 
further  stated  that  a  magnetic  field  exists  around  every  wire  carrying 
an  electric  current  (fig.  10).  The  direction  of  the  lines  of  force  in  this 
field  depends  on  the  direction  of  the  current.  These  lines  of  force  always 
enclose  circles  in  planes  at  right  angles  to  the  wire. 

11.  Since  a  current  is  conceived  to  he  made  up  of  a  quick  succession 
of  moving  electric  charges  (art  3),  the  above  facts  may  be  stated  in 
another  way,  viz.,  that  moving  electric  charges  produce  magnetic  fields 
in  which  the  lines  of  magnetic  force  enclose  circles  in  planes  at  right 
angles  to  the  direction  of  motion  of  the  moving  charges.  This  has  been 
proved  to  be  true  for  single  static  charges.* 

ELECTRO-MAGNETIC  INDUCTION. 

12.  Fig.  11  represents  a  primary  battery,  with  the  two  poles  of  the 
battery  connected  by  a  conducting  wire,  broken  at  K.    A  straight  portion 

*  By  Professor  Rowland,  Johns  Hopkins  University. 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


15 


A  B  of  this  wire  is  parallel  to,  and  at  a  distance  from  another  conducting 
wire  C  D.  When  the  break  at  K  is  closed,  a  current  flows  in  the  circuit, 
and  a  field  of  force  is  created  around  the  wire.  Let  ys  consider  the 
straight  portion  A  B  in  which  the  direction  of  the  current  is  shown  by 
the  arrows,  and  the  direction  of  the  lines  of  force  by  the  circles  (shown 
as  ellipses),  at  right  angles  to  A  B.  Several  of  these  lines  of  force  are 
shown  embracing  the  parallel  wire  C  D. 

If  gold-leaf  electroscopes  (art.  1)  are  attached 
to  the  ends  C  and  D  of  the  wire  C  D,  and  if  the 
current  started  in  A  B  when  the  break  is  closed 
is  sufficiently  powerful,  the  gold  leaves  will  be 
observed  to  diverge,  momentarily,  whenever  the 
circuit  is  made  or  broken  at  K.  The  stronger  the 
current  in  A  B,  and  consequently  the  stronger 
the  magnetic  field  produced,  the  more  pro- 
nounced the  indications  of  the  electroscope  will 
be. 

This  shows  that  the  ends  C  and  D  of  the  wire 
C  D  are  electrified  when  the  current  is  made  or  broken  in  A  B.    When  the 
current  is  made  the  end  D  is  negatively  charged  like  the  amber  and  like 
the  wire  attached  to  the  zinc  element  in  fig.  1,  the  end  C  positively,  like  the 
silk  and  like  the  wire  attached  to  the  carbon  element  in  fig.  1. 

When  the  circuit  is  broken  at  K  the  electrification  of  C  D  is  reversed, 
C  becoming  negatively  and  D  positively  electrified.  A  sudden  increase 
or  decrease  of  the  current  in  A  B  produces  the  same  effect  as  when  the 
current  is  made  or  broken. 

It  is  to  be  noted  that  the  electrification  of  C  D  is  only  momentary. 
As  soon  as  the  causes  producing  it  are  removed,  the  electric  charges 
unite  and  neutralize  each  other  through  the  body  of  the  conductor. 

We  know  that  when  the  current  in  A  B  is  made,  a  magnetic  field  is 
created  around  A  B  which  extends  to  and  beyond  C  D,  and  that  when  the 
current  in  A  B  is  broken,  the  magnetic  field  disappears,  and  that  the 
only  thing  common  to  A  B  and  C  D  is  this  magnetic  field,  the  lines  of 
force  in  which  surround  them  both,  and  since  we  see  that  one  kind  of 
electrification  is  produced  in  C  D  when  the  lines  of  force  are  being 
created,  and  the  opposite  kind  when  they  are  being  dissipated,  we  con- 
clude that  the  movement  or  creation  of  these  lines  creates  the  electric 
charges  that  we  observe  in  C  D. 

13.  In  art.  11  it  is  stated  that  moving  electric  charges  create  magnetic 
lines  of  force.  N"ow,  we  see  the  truth  of  the  converse,  viz.,  that  moving 
magnetic  lines  of  force  create  electric  charges. 

These  two  facts  are  of  general  application  and  are  the  basis  of  all 
electro-magnetic  calculations. 


16 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONT. 


14.  It  is  of  great  importance  to  keep  clearly  in  mind  the  fact  that 
electrification  in  C  D  only  takes  place  when  the  current  is  made  or 
broken  or  changed  in  A  B.  When  there  is  no  current  in  A  B  there  are 
no  magnetic  lines  of  force,  and  consequently  there  is  no  electrification 
in  C  D.  When  there  is  a  constant  current  in  A  B  the  magnetic  field  is 
constant  and  there  is  no  electrification  in  C  D. 

It  is  while  the  current  in  A  B  is  rising  or  falling,  and  the  lines  of 
force  expanding  from  or  contracting  toward  A  B  and  cutting  through 
C  D  as  they  pass,  that  C  D  is  affected.  A  movement  of  the  lines  of  force 
is  required  to  electrify  C  D,  and  this  movement  is  produced  by  changes 
in  the  current  in  A  B. 

If  the  ends  C  and  D  are  joined  to  form  a  complete  circuit,  a  momen- 
tary current  will  flow  when  changes  in  the  magnetic  field  around  C  D 
take  place. 

We  have  just  seen  that  a  moving  magnetic  field  in  the  vicinity  of  C  D 
creates  electric  charges  in  C  D.  We  would  also  find  that  moving  C  D 
in  a  magnetic  field  has  the  same  effect.  The  change  of  current  in  A  B 
is  said  to  induce  the  current  in  C  D,  and  the  action  is  called  electro- 
magnetic induction. 

The  preceding  facts  can  be  stated  as  follows:  When  magnetic  lines 
of  force  cut  or  are  cut  by  a  conductor,  electric  charges  (i.  e.,  a  tendency 
to  current  flow)  are  induced  in  the  conductor,  and  currents  flow  if  the 
conductor  forms  a  closed  circuit,  the  direction  of  the  induced  currents 
depending  on  the  direction  of  cutting. 

15.  When  the  current  in  A  B  is  rising,  tlie  magnetic  lines  of  force 
are  expanding,  and  cutting  C  D  in  the  direction  from  left  to  right,  the 
direction  of  the  momentary  current  in  C  D  being  as  shown  in  fig.  11a. 


Fig.  11a. — Current  in  A-B  Rising. 


B  D 

Fig.  11b.— Current  in  A-B  Falling. 


When  the  current  in  A  B  is  falling,  the  magnetic  lines  of  force  are 
contracting,  and  cutting  C  D  in  the  direction  from  right  to  left,  the 
direction  of  momentary  current  in  C  D  being  shown  in  fig.  lib.  These 
momentary  currents  or  movements  of  electric  charges  in  C  D  themselvee 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


17 


produce  momentary  magnetic  fields  around  C  D,  the  direction  of  the 
lines  of  force  of  which  are  shown  by  the  arrows  in  figs.  11a  and  lib. 
It  will  be  seen  that  the  lines  of  force  around  C  D,  when  the  current  in 
A  B  is  rising,  are  opposite  in  direction  to  those  created  when  the  current 
in  A  B  is  falling.  The  field  of  force  created  around  C  D  reacts  upon 
A  B,  tending  to  create  in  A  B  a  current  in  the  opposite  direction  to  that 
already  in  A  B,  i.  e.,  to  stop  it. 

In  other  words,  the  change  of  primary  current  in  A  B  induces  a 
secondary  current  in  C  D.  The  latter  current  in  turn  induces  a  tertiary 
current,  which  is  in  A  B.  This  influence  of  two  currents  on  each  other 
is  called  their  mutual  induction. 

16.  The  electric  charges  produced  by  friction  (art.  1),  by  chemical 
action  (art.  3),  and  by  the  movement  of  lines  of  magnetic  force  are  all 
identical  in  their  properties,  and  the  magnetic  fields  produced  by  the 
movement  of  these  charges  are  also  identical  in  their  properties.  It  is 
therefore  evident  that  a  very  close  relation  exists  between  electricity  and 
magnetism. 


Pig.  12. 


v''  (^V^Z-^^nV'  '/, 


Fig.  12a. 


Fig.  12c. 

Fig.  12. — Electric  Field  Charges  of  Opposite  Sign. — Attraction. 
Fig.  12a. — Magnetic  Field  between  Unlike  Poles. — Attraction. 
Fig.  12b. — Electric  Field  Charges  of  Same  Sign. — Repulsion. 
Fig.  12c. — Magnetic  Field  between  Like  Poles. — Repulsion. 


17.  We  have  seen  that  the  field  of  magnetic  force  around  a  wire 
carrying  a  current  or  around  a  magnet  can  be  mapped  out  by  iron 
filings.  In  a  similar  manner  the  field  of  electric  force  around  charged 
bodies  can  be  shown  by  the  use  of  a  dielectric,  such  as  powdered  mica. 

Figs.  12  and  12b  show  the  electric  field  between  unlike  and  like 
charges,  respectively.  Figs.  12a  and  12c  show  the  magnetic  field  between 
unlike  and  like  poles,  respectively.  The  electric  field  between  two 
2 


18  MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

charged  bodies  is  found  to  resemble  very  closely  the  magnetic  field  be- 
tween magnet  poles.*  In  all  figures  it  can  be  seen  that  in  electric  as  well 
as  magnetic  fields  each  line  of  force  appears  to  repel  its  neighbor,  and 
that  they  have  their  ends  on  points  of  opposite  electrification  or  magnet- 
ization. If  these  lines  tend  to  shorten  in  the  direction  of  their  length 
this  tendency  will  cause  the  attraction  between  the  bodies  from  which 
they  proceed. 

18.  It  may  be  asked, — what  are  these  lines  of  force  which  are  not 
visible  and  which  can  not  be  physically  grasped?  The  only  reply  is 
that  we  believe  all  electric  and  magnetic  phenomena  to  be  the  results  of 
the  disintegration  of  the  atoms  of  matter  or  the  rearrangement  of 
their  constituent  parts  (see  note  2,  appendix),  the  movements  of  which 
produce  stresses  and  consequent  movement  or  strains  in  what  is  called 
the  ether,  an  almost  infinitely  elastic,  infinitely  tenuous  substance  which 
surrounds  and  permeates  all  matter  and  all  space. 

The  earth  is  immersed  in  an  illimitable  ocean  of  ether,  just  as  fishes 
are  in  water. 

We  move  about  in  a  sea  of  it. 

"What  we  call  electric  and  magnetic  fields  are  places  where  ether  move- 
ments and  ether  stresses  can  be  detected  by  the  phenomena  which  they 
produce,  and  which  are  being  described. 

An  electric  field  is  a  state  of  strain  (stretch  or  compression)  in  the 
ether;  it  can  be  removed  between  any  two  points  by  connecting  them 
with  a  conductor.  The  release  of  the  strain  starts  movements  of  electric 
charges  in  the  conductor.  Movements  of  these  charges  produce  another 
state  of  strain  in  the  ether  at  right  angles  to  the  first.  We  call  this  a 
magnetic  field. 

We  have  seen  that  movement  of  either  field  creates  the  other,  and  that 
the  lines  of  force  in  the  two  fields,  when  they  are  thus  produced,  are  in 
planes  at  right  angles  to  each  other.  When  equilibrium  is  restored  one 
field  or  the  other  has  disappeared,  though  they  can  coexist  in  a  transitory 
state. 

19.  It  lia^  been  proved  thai  light  and  heat  are  forms  of  ether  motion 
also,  and  that  all  movements  (electric  and  magnetic)  in  the  ether  are 
propagated  with  the  velocity  of  light. 

It  has  also  been  proved  that  electric  movements  progress  along  straight 
wires  at  practically  the  same  speed  that  magnetic  movements  progress  at 
right  angles  to  them — i.  e.,  with  the  speed  of  light. 

This  velocity  has  been  measured  many  times  and  found  to  be  186,000 
miles,  or  approximately  SOOfiOOjOOO  meters  per  second. 

*  The  direction  of  the  electric  lines  of  force  at  any  point  in  the  field  can  be 
determined  by  suspending  in  it  a  small  piece  of  a  dielectric,  such  as  a  glass 
fibre.  The  dielectric  will  lie  parallel  to  the  direction  of  the  lines  of  force  at  the 
point  of  suspension. 


MANUAL    OF    RADIO    TELEGRAniY    AND   TELEPHONY.  19 

We  must  learn  therefore  to  think  of  light  movements  and  of  electric 
and  magnetic  actions  not  as  being  instantaneous,  but  as  being  restricted 
to  a  definite  measurable  speed. 

It  takes  time  for  electric  and  magnetic  effects  to  be  propagated  in  the 
ether,  time  for  them  to  be  propagated  along  a  wire.  The  wire  guides  or 
strikes  out  the  line  of  maximum  disturbance. 

20.  Let  us  now  return  to  fig.  11.  Before  connection  at  K  is  made, 
the  field  of  magnetic  force  does  not  exist,  but  the  wires  are  electrified 
by  means  of  action  between  the  zinc  and  carbon  in  the  battery  solution. 
When  the  break  at  K  is  closed,  a  magnetic  field  is  established;  when  the 
connection  at  K  is  broken,  the  magnetic  field  disappears.  The  question 
arises, — how  is  this  magnetic  field  created?  How  is  it  dissipated?  The 
reply  is:  It  is  created  by  movements  of  electric  charges  in  A  B  which 
disturb  the  ether  and  this  disturbance  is  propagated  through  the  ether 
at  right  angles  to  A  B,  with  the  speed  of  light,  i.  e.,  at  the  rate  of  186- 
000  miles  or  300,000,000  meters  per  second.  This  disturbance  is  of  such 
a  nature  as  to  produce  a  state  of  strain  in  the  ether  which  may  be 
compared  to  that  produced  in  a  piece  of  rubber  by  compression  or 
tension.  The  strain  is  relaxed  as  soon  as  its  cause  (i.  e.,  the  movement 
of  the  electric  charges)  is  removed. 

The  amount  of  strain  (i.  e.,  the  strength  of  the  magnetic  field) 
decreases  as  the  distance  from  the  moving  charges  increases.  It  spreads 
in  all  directions,  but  except  with  very  delicate  instruments  can  not  be 
detected  at  any  great  distance  from  A  B. 

The  creation  and  dissipation  of  this  state  of  unstable  equilibrium 
in  the  ether,  which  must  be  brought  about  by  some  kind  of  movement 
in  it,  produce  electrical  movement  in  C  D,  or,  as  it  is  perhaps  better 
to  say,  produce  electric  charges  in  C  D.  CD  stands  in  the  way  of  and 
is  disturbed  by  an  advancing  or  receding  wave  of  movement  in  the  ether, 
originated  at  A  B.  CD  is,  like  all  other  conductors,  an  obstacle  in  the 
path  which  creates  an  eddy,  so  to  speak,  in  the  ether  wave  and  reacts, 
however  minutely,  on  A  B,  because  the  movement  of  the  electric  charges 
produced  in  C  D  also  creates  an  ether  movement,  but  in  the  opposite 
direction  to  that  proceeding  from  A  B. 

21.  We  have  now  reached  a  point  where  the  electric  and  magnetic 
actions  under  discussion  are  directly  applicable  to  wireless  telegraphy, 
but,  before  proceeding  with  this  subject,  it  is  desirable  to  consider  more 
fully  the  action  of  A  B  on  C  D ;  because  the  creation  of  electric  currents 
by  moving  or  varying  magnetic  fields,  and  vice  versa,  is  the  basis  of 
industrial  electric  power — of  that  used  in  wireless  telegraphy  as  well 
as  in  other  branches  of  electricity;  and  other  facts  or  developments  of 
this  fundamental  fact  will  appear  which  will  lead  to  a  clearer  compre- 
hension of  it. 


20 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


Fig 


22.  In  fig.  11,  C  D  is  shown  parallel  to  A  B. 

^x  If  C  D  is  slowly  revolved  around  its  own  center 

^5-r^^  ^^^^  as  an  axis  the  effect  on  it  of  making,  breaking, 
'','?'/' crtffC-^^i^^^f^mF^,  or  changing  the  current  in  A  B  will  be  found  to 
decrease  until  C  D  is  at  right  angles  to  A  B, 
,|^  when  it  will  disappear  altogether.  The  lines  of 
force  are  circles  at  right  angles  to  A  B ;  they  do 
not  cut  C  D  when  it  is  at  right  angles  to  A  B 
because  it  is  parallel  to  them,  and  consequently 
no  effect  is  produced. 

The  induced  effects  in  C  D  will  be  found  to 
increase  as  it  is  brought  nearer  A  B  and  to  decrease  as  it  is  removed 
from  A  B.  The  field  near  A  B  is  stronger,  and  more  lines  of  force  are 
created  there  or  dissipated  there  than  at  a  greater  distance  from  A  B — 
i.  e.,  a  greater  disturbance  in  the  ether  takes  place. 

23.  If  the  two  ends  of  C  D  (fig.  11),  are  brought  close  together,  but 
without  touching,  and  if  the  current  made  or  broken  in  A  B  is  very 
strong,  a  spark  will  pass  between  the  ends  of  C  D  at  each  make  and 
break.  If  C  D  is  separated  from  A  B  by  an  opaque,  nonmetallic  screen 
and  the  makes  or  breaks  in  A  B  are  made  to  represent  the  characters  of 
a  code,  messages  sent  in  this  code  from  A  B  can  be  received  at  C  D 
when  each  is  invisible  from  the  other.  By  the  addition  of  a  battery  to 
C  D,  similar  to  that  producing  current  in  A  B,  replies  can  be  sent,  and 
thus  a  crude  wireless  telegraphy  produced. 

24.  If  A  B  is  coiled  into  a  spiral  or  helix  and  C  D  into  a  similar  spiral 
or  helix  (fig.  13),  the  effect  of  making,  breaking,  or  changing  the  current 
in  A  B  is  much  greater  than  when  both  wires  are  straight;  for  the 
disturbance  created  in  the  ether — that  is,  the  number  of  lines  of  force 
produced  by  the  moving  charges  in  A  B — is  equal,  for  equal  lengths  of 
the  wire,  and  since  a  greater  length  is  concentrated  in  the  same  space, 
the  number  of  lines  of  force  in  that  space,  assuming  the  current  in  the 
spiral  to  be  the  same  as  that  in  the  straight  wire,  is  correspondingly 
greater.  This  stronger  field  would  produce  an  increased  effect  on  a 
straight  wire;  but  the  length  of  C  D  is  also  concentrated.  Therefore 
the  effect  is  increased  still  more. 

25.  We  know  that  A  B  when  coiled  as  in  fig.  13  and  traversed  by  a 
current  forms  a  solenoid  (art.  8,  fig.  8).  The  space  inside  the  coil  is 
called  the  core,  and  it  has  been  assumed  that  the  surrounding  substance 
(excluding  the  ether,  which  is  present  both  in  the  interior  and  on  the 
exterior  of  all  bodies)  is  air.  It  is  found,  however,  that  if  the  core  of 
the  solenoid  is  iron,  as  in  fig.  14,  instead  of  air,  the  effect  on  C  D  is  very 
much  more  powerful — i.  e.,  the  number  of  lines  of  force  created  with  the 
same  current  is  very  greatly  increased. 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


21 


This  shows  that  it  is  easier  to  create  lines  of  force  in  iron  than  in  air; 
or,  to  state  the  fact  differently,  lines  of  force  permeate  iron  more  easily 
than  they  do  air.  The  relative  ease  with  which  magnetic  lines  of  force 
are  created  in  a  substance  is  expressed  in  figures  and  called  its  magnetic 
permeability.    The  permeability  of  air  at  atmospheric  pressure  is  called 

CUKf^ENT   IN  A-B  RISING^ 


=g^ 


unity,  and  on  that  basis  the  permeability  of  the  purest  wrought  iron  is 
3,000.  In  other  words,  within  limits  the  same  current  will  produce  3,000 
times  as  many  lines  of  force  in  iron  as  in  a  body  of  air  of  the  same 
length  and  area  of  cross  section. 


CURRENT 


-< c 


->-     D 


Fig.  14. 


26.  If  the  iron  of  fig.  14  is  extended  to  include  C  D,  as  in  fig.  14a,  the 
effect  of  changes  in  A  B  is  increased  still  more,  because  in  fig.  14  the 
lines  of  force  are  partly  in  iron  and  partly  in  air,  while  in  fig.  14a  they 
have  an  iron  path  throughout,  and  are  consequently  much  greater  in 
number.  C  D  can  also  be  placed  inside  of  A  B  or  outside  of  it,  with 
or  without  an  iron  core  (figs.  14b  and  14c). 


22 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


Fig.  14a. — Closed-Core  Transformer  (current  in  A  B  falling). 

<"-  ^ 


1 


Fig.  14b. — Open-Core,  Step-Down  Transformer  or  Induction  Coil 
(current  in  A  B  rising). 

C 


Fig.  14c. — Air-Core,  Step-Up  Transformer  (current  in  A  B  rising). 
-< A C 


"B D »- 

Fig.  14d. — Auto  Step-Down  Transformer  (current  in  A  B  rising). 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


23 


27.  Since  the  tendency  to  current  flow  in  C  D  is  produced  by  lines 
of  magnetic  force  cutting  C  D,  and  since  on  making  or  breaking  cur- 
rent in  A  B  each  line  of  force  cuts  C  D  once,  for  each  turn  in  C  D,  if 
the  turns  in  C  D  are  decreased  or  increased,  as  in  figs.  14b  and  14c,  the 
tendency  to  current  flow — i.  e.,  the  electro-motive  force — is  raised  or 
lowered.  From  this  fact,  and  from  the  fact  that  the  current  in  C  D  is 
opposite  in  direction  to  that  in  A  B,  the  arrangements  in  figs.  14a,  14b, 
and  14c  are  called  transformers.  Fig.  14a  is  called  a  closed-core  trans- 
former; fig.  14b  an  open-core  transformer  or  induction  coil;  fig.  14c  an 
air-core  transformer. 

Transformers  are  called  step-up  or  step-down  with  reference  to 
whether  the  turns  in  the  coil  C  D  are  greater  or  less  than  those  in  A  B. 
Fig.  14b  is  a  step-down;  fig.  14c  a  step-up  transformer.  The  coil  A  B 
is  called  the  primary  and  the  coil  C  D  the  secondary  winding,  and  where 
A  B  and  C  D  have  some  turns  common  to  both,  as  in  fig.  14d,  the 
arrangement  is  called  an  auto-transformer. 


=^ 


Fig.  13. 


28.  Keferring  again  to  fig.  13 :  When  the  break  at  K  is  closed,  a 
current  is  started,  which  progresses  upward  through  the  coil,  the  mov- 
ing charges  composing  it  creating  a  magnetic  field  around  the  wire. 
The  lines  of  force,  as  they  expand  from  the  current  in  the  first  turn  of 
the  spiral,  cut  the  second  turn  of  A  B  in  the  same  way  that  they  cut 
C  D  a  little  later.  They  induce  a  current  in  the  second  turn  opposite 
in  direction  to  that  in  the  first  turn — i.  e.,  tending  to  stop  it.  The  same 
effect  is  produced  in  the  third  and  succeeding  turns.  In  other  words, 
the  different  parts  of  the  coil  A  B  react  on  each  other  just  as  the  coil 
C  D  reacts  on  A  B.  This  reactive  effect  of  the  turns  on  each  other 
makes  the  rise  in  current  slower  than  in  a  straight  wire,  and  is  greater 
when  the  core  of  the  coil  is  of  iron  than  when  it  is  of  air,  because  of  the 
greater  number  of  lines  of  force  produced. 


24  MANUAL   OF    RADIO    TELEGRAPHY    AND    TELEPHONY. 

29.  We  find  that  a  stronger  current  is  produced  by  the  same  battery 
in  a  short  wire  than  in  a  long  wire  of  the  same  size  and  material,  and  in 
a  thick  wire  than  in  a  thin  wire  of  the  same  length,  and  we  say  that  this 
is  due  to  the  greater  resistance  of  the  long  wire  and  of  the  thin  wire  as 
compared  with  the  short  or  with  the  thick  wire.  To  establish  the  same 
current  in  the  longer  or  the  thinner  wire  as  in  the  shorter  or  thicker 
wire  requires  a  larger  battery — that  is,  greater  E.  M.  F. 

30.  Now,  we  find  that  when  the  wire  is  coiled  into  a  spiral  and  a 
change  in  the  current  is  taking  place,  the  turns  react  on  each  other  and 
resist  the  change  of  the  current.  This  resistance  does  not  depend  on 
the  size  nor  the  material  of  the  wire,  but  only  on  the  amount  and  quick- 
ness of  the  change  in  the  current,  and  is  therefore  of  a  different  character 
from  the  resistance  referred  to  above.  The  resistance  of  a  wire  to  changes 
in  current  established  in  it  is  called  its  reactance,  and  during  the  change 
the  total  effect  of  the  true  resistance  and  the  reactance  is  called  the 
impedance  of  the  wire  or  circuit. 

In  circuits  having  reactance  tlie  production  or  progression  of  electrical 
effects  is  retarded.  It  takes  longer  to  create  a  given  current  than  in  the 
same  length  of  straight  wire.  It  may  be  said,  therefore,  that  coiling  a 
wire  increases  its  electrical  length — i.  e.,  increases  the  time  it  takes  an 
electrical  movement  created  at  one  end  of  it  to  reach  the  other. 

The  currents  in  C  D  are  said  to  be  produced  by  the  induction  of  A  B 
on  C  D.  The  retarding  effect  of  the  coils  in  A  B  to  the  rise  and  fall  of 
current  in  A  B  is  said  to  be  due  to  the  self-induction  of  A  B.  It  has 
been  shown  that  the  amount  of  both  kinds  of  induction  depends  on  the 
shape  and  arrangement  of  both  circuits  and  the  material  (iron  or  air) 
in  and  around  them. 

RELATION  OF  POSITIVE  DIRECTION  OF  LINES  OF  FORCE  TO  POSITIVE 
DIRECTION  OF  CURRENT. 

31.  The  currents  under  discussion  have  been  illustrated  as  being  pro- 
duced by  batteries  of  primary  cells,  and  for  many  purposes  these  are 
very  valuable,  but  for  the  production  of  very  powerful  electrical  effects 
advantage  is  taken  of  the  fact,  stated  in  art.  14,  that  when  magnetic 
lines  of  force  cut  or  are  cut  by  a  conductor,  electric  currents  flow  in  the 
conductor,  if  the  latter  forms  a  closed  circuit. 

The  direction  of  current  flow  can  be  determined  by  the  following  rules  :* 
(a)  Fig.  15.  An  increase  in  the  number  of  lines  of  force  embraced  by  a 
circuit  induces  a  current  in  the  opposite  direction  to  that  in  which  the 
hands  of  a  watch  move,  while  a  decrease  in  the  number  of  lines  of  force 
induces  a  current  in  the  same  direction  as  that  in  which  the  hands  of  a 
watch  move,  the  line  of  sight  being  in  both  cases  along  the  positive  direc- 

•  Rule   (a)   from  Fiske's  "Electricity  and  Electrical  Engineering." 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


25 


tion  of  the  liues  of  force.  (Art.  7  and  fig.  7.)  (b)  The  positive  direc- 
tion of  the  lines  of  force  is  with  the  hands  of  a  watch  when  the  current 
is  flowing  away  from  the  observer.  Fig.  15a.  (c)  The  currents  induced 
by  moving  lines  of  force  always  tend  to  prevent  change  in  the  inducing 
current.  Induced  currents  are,  therefore,  in  the  opposite  direction  when 
the  inducing  current  is  rising  and  in  the  same  direction  as  the  inducing 
current  when  the  latter  is  falling.     (Art.  15.) 

From  rules  (b)  and  (c)  can  be  deduced  the  following:  Let  fig.  15b 
represent  a  conducting  wire  C  D  below  a  line  N  S,  which  represents  a 
field  of  force  and  its  direction.  When  in  the  relative  positions  shown, 
movement  of  either  wire  or  line  of  force  toward  the  other  creates  a  current 
to  the  rear,  moving  either  one  away  from  the  other  creates  a  current  to 
the  front. 


/   : 


N 


£. 


JT^ 


7 


=j 


D    I r 


D  D 

Fig.  15a.        Fia.  15b. 


Fig.  15. 

It  will  be  seen  that  the  field  N  S  can  be  revolved  through  any  angle 
around  the  wire  C  D  as  an  axis  so  as  to  be  to  the  right,  left,  helow  or 
in  any  intermediate  position  without  changing  the  truth  of  the  above 
statement. 

These  three  rules  show  the  relation  between  what  we  call  the  positive 
direction  of  the  lines  of  magnetic  force  and  what  we  call  the  positive 
direction  of  electric  current. 


METHOD  OF  PRODUCING  CURRENTS  BY  ELECTRO-MAGNETIC  INDUCTION. 

32.  Now  let  the  wire  C  D  in  fig.  11  be  bent  until  it  forms  a  rectangle, 
and  let  it  be  placed  in  the  magnetic  field  between  the  north  and  south 
poles  of  a  powerful  electro-magnet  having  an  iron  core.  By  bending  the 
core  into  the  shape  shown  in  fig.  16,  the  north  and  south  poles  are  oppo- 
site each  other  and  more  lines  of  force  are  produced,  because  the  distance 


36 


MANUAL    OF    RADIO    TELKGRAPHY    AXD    TELEPHONY, 


they  have  to  travel  through  the  air  is  very  much  shortened  as  compared 
with  fig.  14. 

Exploration  of  the  field  in  fig.  16  by  means  of  iron  filings  or  by  means 
of  a  small  magnetic  needle  will  show  that  the  lines  of  force  extend 
directly  from  a  point  in  the  north  pole  to  the  opposite  point  in  the 
south  pole.  In  other  words,  that  they  are  straight  and  parallel  to  each 
other,  and  they  are  so  shown  in  fig.  16.  The  field  is  also  found  to  be  of 
uniform  intensity,  which  indicates  that  the  lines  of  force  are  equally  dis- 
tributed throughout  its  area. 

Now,  if  C  D  is  moved  up  or  down  in  the  magnetic  field,  no  indica- 
tion of  a  current  can  be  perceived,  and  it  appears  that  the  statement  in 
art.  14  (that  when  magnetic  lines  of  force  cut  or  are  cut  by  a  conductor 


^kMb 


Fig.  16. 


electric  currents  flow  in  the  conductor  if  the  latter  forms  a  closed  circuit) 
is  in  error,  but  when  we  consider  that  when  C  D  is  moved  upward  (the 
field  being  of  unifonn  intensity)  as  many  lines  of  force  are  cut"  by  the 
bottom  half  as  by  the  top  half  of  C  D,  the  currents  induced  in  the  two 
halves  must  therefore  be  equal,  and  since  both  flow  to  the  rear  we  see 
that  they  neutralize  each  other,  and  the  result  is  zero.  Another  way  to 
explain  this  is  to  consider  that  portion  of  the  field  inclosed  by  C  D  as 
containing  a  certain  number  of  lines  of  force.  Those  coming  in  when 
C  D  is  moved  induce  a  current  in  one  direction,  those  going  out  induce 
a  current  in  the  opposite  direction,  and  if  as  many  come  in  as  go  out  no 
effect  is  produced. 

33.  If  C  D  were  straight,  electric  charges  would  be  produced  on  its 
ends  and  would  be  maintained  there  as  long  as  the  cutting  of  the  lines 
of  force  continued,  but  bending  it  into  a  closed  circuit  changes  conditions 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


27 


to  the  extent  that  cutting  of  lines  is  going  on  all  around  the  circuit, 
Boine  inducing  charges  in  one  direction,  some  in  the  other,  and  it  is 
only  when  there  is  a  preponderance  of  cutting  in  one  direction  that  a 
current  actually  flows.  This  would  occur  if  C  D  were  moved  from  a 
point  where  the  field  is  weak  to  where  it  is  stronger,  or  vice  versa,  but 
the  field  under  discussion  is  supposed  to  be  uniform.   (See  rule  a,  art.  31.) 

If  C  D  is  rotated  around  one  of  its  diameters  as  an  axis  (say  the  hori- 
zontal diameter  at  right  angles  to  the  lines  of  force)  when  it  is  hori- 
zontal, as  in  fig.  17,  the  lines  of  force  included  will  be  zero,  and  when 
vertical,  as  in  fig.  17a,  the  lines  of  force  included  will  be  the  maximum 
number  possible  in  that  field,  so  that  a  revolution  of  90°  will  make  an 
entire  change  in  the  number  of  lines  of  force  passing  through  the 
rectangle. 

For  instance,  if  the  revolution  is  in  the  direction  of  the  hands  of  a 
clock — i.  e.,  if  the  top  of  C  D  moves  to  the  right  (see  fig.  17a) — the 
upper  half  of  C  D  is  cutting  lines  of  force  in  the  direction  which  induces 
movements  of  electric  charges  to  the  front,  while  the  lower  half  is  cutting 


Fig.  17. 


Fig.  17a, 


lines  of  force  in  the  direction  which  induces  movements  of  electric 
charges  to  the  rear,  so  that  an  electric  current  is  established  in  C  D  in 
the  direction  shown,  the  number  of  lines  of  force  included  in  C  D  is 
decreasing,  and  looking  from  N  to  S,  the  current  moves  with  the  hands 
of  a  watch. 

If  C  D's  rate  of  revolution  is  constant,  a  little  consideration  will  show 
that  when  it  has  revolved  through  90°  and  its  plane  is  horizontal  it 
is  then  moving  at  right  angles  to  the  lines  of  force,  and  consequently 
cutting  them  faster  than  when,  its  plane  being  vertical,  it  moves  parallel 
to  the  lines  of  force  for  an  instant  and  is  not  cutting  any;  also  that 
the  increase  in  the  rate  of  cutting  is  progressive  from  one  position  to  the 
other.  It  will  therefore  be  seen  that  the  electric  current  produced  is  a 
maximum  when  C  D  is  horizontal,  and  that  it  is  zero  for  an  instant 
when  C  D  is  vertical  because  during  that  instant  it  moves  parallel 
to  the  lines  of  force  and  therefore  it  cuts  none.  (No  change  in  number 
included.)  It  is  also  evident  that  the  increase  of  the  current  from  zero 
to  a  maximum  is  progressive  during  the  first  90°  of  revolution,  that  it 
then  progressively  decreases  until  C  D  has  revolved  through  180°,  and 
IB  again  moving  parallel  to  the  lines  of  force  when  it  falls  to  zero. 


28 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


As  the  revolution  continues,  that  half  of  C  D  which  during  the  first 
half  revolution  was  cutting  lines  of  force  in  such  a  manner  as  to  induce 
a  current  to  the  front,  now  cuts  them  in  such  a  manner  as  to  induce  a 
current  to  the  rear,  its  former  place  being  taken  by  what  was  originally 
the  lower  half,  so  that  the  direction  of  current  in  C  D  is  reversed. 
(Eule  c.) 

Another  maximum  rate  of  cutting  lines  of  force  and  consequent  maxi- 
mum of  current  is  produced  when  C  D  has  revolved  through  270°,  The 
current  progressively  increases  from  180°  to  270°  and  then  decreases 
until  when  the  original  conditions  are  restored  by  the  completion  of  one 
revolution  the  current  has  again  fallen  to  zero. 

From  the  above  and  from  an  inspection  of  fig.  17a  it  will  be  seen  that 
current  is  always  flowing  to  the  front  in  that  half  of  C  D  which  is  going 
down  to  the  right  and  to  the  rear  in  the  half  going  up  on  the  left,  and 
that  each  half  revolution  the  current  changes  in  direction.  Such  a  cur- 
rent is  called  an  alternating  current. 


Fig.  18. 


34.  This  can  be  shown  graphically  in  fig.  18,  where  the  rate  of  cut- 
ting and  therefore  the  rate  of  change  of  number  of  lines  included  in  the 
circuit  at  different  equidistant  points  in  one  revolution  is  represented  by 
equidistant  vertical  lines  proportional  to  the  cutting  rate,  and  conse- 
quently to  the  current  strength.  Vertical  lines  above  the  horizontal  line 
represent  current  strength  in  one  direction  and,  below  it,  current  strength 
in  the  opposite  direction.  A  regular  curve  is  produced  by  joining  the 
tops  of  these  lines.  This  curve  is  the  curve  of  sines,  because  the  rate  of 
cutting  and  the  strength  of  the  induced  current  are  proportional  to  the 
sine  of  the  angle  of  revolution.* 

*  Since  the  lines  of  force  are  horizontal,  the  number  cut  during  the  revolu- 
tion of  C  D  through  any  angle  is  proportional  to  the  vertical  movement  of  the 
extremity  of  the  radius  of  C  D  which  generates  the  angle.  The  amount  of 
this  vertical  movement  is  the  sine  of  the  angle,  and  therefore  the  induced 
current  is  proportional  to  the  sine  of  the  angle;  also  and  for  the  same  reason 
the  induced  E  M  F  which  produces  the  current  is  proportional  to  the  sine  of 
the  angle  of  revolution. 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


29 


35.  If  C  D,  instead  of  forming  a  closed  circuit  entirely  in  the  mag- 
netic field  has  its  ends  connected  to  two  rings  which  revolve  with  it  and 
touching  these  rings  are  the  ends  of  a  coiled  wire  (E  F,  fig.  19),  the 


currents  induced  in  C  D  also  flow  through  E  F  and  make  of  it  a  sole- 
noid whose  strength  varies  with  the  strength  of  the  current  and  whose 
polarity  reverses  with  the  reversal  of  the  current.  If  a  small  magnetic 
needle  were  pivoted  in  E  F,  its  direction  would  tend  to  change  with  each 
reversal  of  the  current,  and  it  can  thus  be  made  to  indicate  both  the 
direction  and  the  amount  of  current  flowing  through  the  coil  E  F.  Such 
an  instrument  is  called  a  galvanometer. 

The  currents  in  the  coil  E  F  are  supplied  from  C  D,  and  they  are 
induced  in  C  D  by  its  movement  in  a  magnetic  field.  C  D  has  become 
a  source  of  electricity  like  the  battery  in  A  B.  E  F  corresponds  to  the 
coil  A  B  in  fig.  13,  and  the  rise  and  fall  of  current  in  E  F  will  produce 
a  rise  and  fall  of  current  in  another  coil  near  it,  just  as  the  make  or 
break  at  K  in  fig.  13  induces  a  momentary  current  in  C  D. 

The  currents  in  C  D,  fig.  13,  were  induced  by  interrupted  current. 
Those  induced  by  E  F  in  coils  near  it  are  induced  by  alternate  current. 
Interrupted  current  was  used  almost  entirely  in  wireless  telegraphy  in 
its  earlier  development.     It  has  now  been  replaced  by  alternate  current. 

36.  It  only  remains  now  to  make  C  D  produce  the  magnetic  field 
in  which  it  revolves,  and  we  can  dispense  entirely  with  the  primary 
battery  in  A  B.    This  can  be  done  as  follows : 

In  fig.  20,  instead  of  having  each 
end  of  C  D  connected  to  a  ring  of 
conducting  material,  as  in  fig.  19, 
one  ring  is  removed  and  the  other 
split  into  two  equal  parts  and  an  end 
of  C  D  connected  to  each  part,  the 
ends  of  E  F  being  adjusted  so  that,  as 
the  split  ring  revolves  with  C  D,  one 
end   of   E    F   is   always   connected  Fia.  20. 


30 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


through  the  split  ring  with  that  half  of  C  D  in  which  the  current  is  flow- 
ing to  the  front  and  the  other  end  to  that  half  in  which  the  current  is 
flowing  to  the  rear.  This  arrangement  makes  the  current  in  E  F  always 
flow  in  the  same  direction.  It  rises  and  falls  with  the  current  in  C  D,  but 
does  not  reverse,  because  just  as  the  current  reverses  in  C  D,  E  F  changes 
ends,  so  to  speak,  by  breaking  connection  with  one  half  of  the  split  ring 
and  making  connection  with  the  other.  The  current  in  E  F  is  now  said 
to  be  a  pulsating  instead  of  an  alternating  current,  and  the  change  can  be 
graphically  represented  by  transferring  the  part  of  the  curve  below  the 
line  in  fig.  18  to  a  corresponding  position  above  it,  as  in  fig.  18a. 


Fig.  18a. 

The  alternating  current  in  C  D  is  said  to  be  rectified  into  a  direct 
current  in  E  F.  The  split  ring  by  means  of  which  it  is  rectified  is  called 
a  commutator,  and  the  entire  apparatus  (either  with  or  without  a  com- 
mutator), a  dynamo. 

37.  With  a  single  coil,  C  D,  rotating  in  the  magnetic  field,  the  current 
in  E  F  can  be  made  to  flow  always  in  the  same  direction,  but  in  order  to 
make  it  constant  a  large  number  of  coils,  equally  spaced,  must  be  used, 
so  that  one  of  them  is  passing  through  the  position  (horizontal)  in 
which  maximum  current  is  produced  practically  all  the  time.  If  there 
were  10  such  coils,  each  connected  to  its  own  split  ring  (fig.  21),  and 
all  connected  to  E  F,  the  currents  in  each  would  overlap,  so  that  the 
resultant  current  in  E  F  (to  another  scale)  might  be  indicated  by  a  line 
joining  the  highest  point  of  each  (fig.  18b).  In  other  words  the  current 
in  E  F  is  practically  constant. 


Fig.  18b. 

The  revolving  coils  are  held  in  place  on  a  cylindrical  drum  or  ring 
and  the  whole  is  called  an  armature.  If  this  ring  is  made  of  iron,  the 
strength  of  the  magnetic  field  is  much  increased,  because  the  iron  affords 
a  path  for  the  lines  of  force  from  one  pole  to  the  other  and  thereby 
lessens  the  distance  through  which  they  have  to  pass  in  the  air.  (See 
art.  25.) 


MANUAL    OF    GADIO    TELEGRAPHY    AND   TELEPHONY. 


31 


The  tendency  to  current  flow  in  C  D  created  by  cutting  lines  of  force 
is  called  the  electro-motive  force  in  C  D  (see  art,  3),  and  is  found  to 
depend  on  the  number  of  lines  cut  in  a  given  time,  so  that  the  faster 
C  D  revolves,  and  the  stronger  the  magnetic  field,  the  greater  the  electro- 
motive force  and  the  greater  the  current  produced  in  any  given  circuit. 
Now,  if  the  current  induced  in  C  D,  instead  of  all  flowing  through  E  F, 
is  divided,  so  that  part  of  it  flows  around  the  core  of  the  electro-magnet 
(fig.  21),  this  current  can  take  the  place  of  that  produced  by  the  battery 
in  A  B  and  the  battery  can  be  dispensed  with. 


Fig.  21. 


38.  In  art.  6  it  is  stated  that  wrought  or  soft  iron  can  be  magnetized, 
but  only  retains  its  magnetism  while  under  the  influence  of  the  magnet- 
izing force.  Steel  or  hard  iron  once  magnetized  retains  its  magnetiza- 
tion permanently  and  special  means  to  demagnetize  it  are  required.  It 
is  found  that  electro-magnets  with  soft-iron  cores  can  be  made  more 
powerful  (i.  e.,  will  give  a  stronger  field)  than  if  the  cores  are  of  steel, 
and  that  electro-magnets  with  either  kind  of  core  can  be  made  to  give 
much  stronger  fields  than  any  permanent  magnet.  Also,  that  soft-iron 
cores  retain  a  very  small  part  of  their  magnetism  and  polarity  when  the 
current  is  broken,  so  that,  if  the  magnet  poles  between  which  C  D 
revolves  are  made  of  the  most  efficient  material  (wrought  iron  or  mild 
steel  containing  no  phosphorus),  when  C  D  stops  they  still  retain  their 
polarity  in  a  slight  degree. 

When  C  D  starts  to  revolve  again,  the  weak  field  generates  a  small  cur- 
rent in  C  D,  which  sends  this  current  through  the  wire  around  the  poles; 
this  current  increases  the  strength  of  the  poles  and  consequently  of  the 
field,  which  increases  the  current  in  C  D  and  so  on.  This  is  called 
generating  or  building  up,  and  continues  until  the  limit  of  the  power 
moving  C  D  in  the  continually  strengthening  field  is  reached,  or  until 
the  iron  core  is  saturated,  in  which  condition  no  increase  of  current  will 
increase  the  field. 


32  MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

39.  When  alternating  current  is  desired,  a  dynamo,  in  order  to  be 
self-exciting,  i.  e.,  to  produce  its  own  field,  must  have  part  of  its  cur- 
rent rectified  by  means  of  a  commutator.  It  is  more  usual,  however, 
to  drive  a  small,  direct-current  dynamo  by  means  of  the  same  power 
which  drives  the  larger  one,  the  current  from  the  small  dynamo  being 
used  to  create  the  magnetic  field  in  the  larger  one.  Such  a  machine  is 
called  an  exciter. 

40.  The  fact  that  magnet  poles  of  unlike  polarity  attract  each  other 
(art.  6)  applies  to  electro-magnets,  with  or  without  iron  cores,  as  well 
as  to  permanent  magnets.  Hence  two  electro-magnets  placed  as  in  fig. 
13  will  attract  or  repel  each  other  according  to  their  polarity.  Each  line 
of  force  apparently  tends  to  contract  in  the  direction  of  its  length,  and 
by  so  doing  exerts  a  mechanical  pull  on  the  conductors  which  it  sur- 
rounds. 

The  same  effect  is  observed  between  a  magnet  and  a  wire  carrying  a 
current  (which,  as  we  know,  has  a  magnetic  field  around  it)  and  between 
two  wires,  each  carrying  a  current.  They  actually  pull  or  push  each 
other  according  to  the  quality  of  their  magnetism,  which  is  determined 
by  the  direction  of  the  current. 

41.  If  in  fig.  21  the  armature  instead  of  being  revolved  to  the  right  by 
some  outside  agency,  is  supplied  with  a  current  flowing  through  it  in  the 
same  direction  as  the  current  it  generates,  it  will  revolve  to  the  left. 

The  current  flowing  to  the  front  in  the  winding  of  the  right  half  of 
the  armature  and  to  the  rear  in  the  winding  of  the  left  half,  makes  of  the 
armature  an  electro-magnet  with  a  north  pole  at  the  bottom  and  a  south 
pole  at  the  top.  The  revolution  is  caused  by  the  attraction  of  the  north 
pole  of  the  armature  by  the  south  pole  of  the  field  m.agnet,  and  its  repul- 
sion by  the  north  pole  of  the  field  magnet.  This  action  is  reversed  in  the 
south  pole  of  the  armature. 

The  movement  will  be  continuous,  because,  as  the  top  of  the  arma- 
ture moves  toward  the  north  pole  of  the  field  magnet,  the  commutator 
acts  to  maintain  the  flow  of  current  as  before,  and  the  consequent  arma- 
ture poles  are  always  at  the  top  and  bottom  halfway  between  the  field 
magnets. 

The  armature  thus  creates  a  current  when  made  to  revolve,  and 
revolves  when  supplied  with  current. 

In  the  first  instance  we  have  seen  tliat  the  entire  machine  is  called 
a  dynamo;  in  the  second  it  is  called  a  motor.  Every  dynamo  will  run 
as  a  motor  if  supplied  with  current.  Every  motor  will  act  as  a  generator 
or  dynamo  if  made  to  revolve  in  its  own  field. 

The  motor  can  be  made  to  drive  another  armature  in  another  field. 
Such  a  machine  is  called  a  motor-generator.  It  can  be  run  with  direct 
or  alternating  currents  and  made  to  srenerate  direct  or  alternating  cur- 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY.  33 

rents  of  a  higher  or  lower  E.  M.  F.  For  this  reason  it  is  sometimes 
called  a  rotary  transformer,  as  distinguished  from  the  stationary  trans- 
formers already  described. 

42.  Electricity  produced  by  friction  (art.  1)  is  sometimes  called  fric- 
tional  electricity;  by  primary  batteries,  voltaic  electricity;  by  electro- 
magnetic induction,  dynamic  electricity.  But  however  produced  and 
transformed,  all  kinds  of  electricity  are  identical,  and  the  same  is  true 
of  all  kinds  of  magnetism. 

PRODUCTION   OF   ELECTRIC   AND   MAGNETIC   FIELDS    STRESSES   AND   STRAINS 

IN  THE  ETHER. 

43.  Wherever  there  is  an  electric  charge,  stationary  or  moving,  emanat- 
ing from  the  charge  are  electric  lines  of  force  which  end  at  other  electric 
charges  and  which  form  electric  fields.  Wherever  there  are  moving  electric 
charges  (currents)  there  are  magnetic  lines  of  force  also,  which  form 
magnetic  fields  and  these  magnetic  lines  of  force  are  always  at  right  angles 
to  the  direction  of  the  motion  of  the  electric  charges  and  to  the  electric 
lines  of  force  proceeding  from  them. 

Motion,  or  state  of  strain  in  the  ether,  which  these  lines  of  force  repre- 
sent, travels  with  the  speed  of  light,  and  the  fields  of  force,  while  more 
pronounced  and  therefore  more  easily  detected  near  the  moving  charges, 
are  really  all  pervasive.    They  have  no  limits. 

Imagine  a  disturbance — say  an  expansion  of  a  gas — to  take  place  in  the 
center  of  an  immense  rubber  ball.  A  wave  of  tension,  which  becomes  less 
as  its  distance  from  the  center  increases,  progresses  outward  through  the 
rubber  to  the  farthest  confines  of  the  ball.  When  the  gas  contracts,  a  wave 
of  contraction,  also  starting  from  the  center,  and  decreasing  with  its 
distance  from  the  center,  progresses  outward  through  the  rubber  to  the 
farthest  confines  of  the  ball.  If  expansion  and  contraction  are  equal  the 
ball's  former  state  of  equilibrium  is  restored. 

In  this  way  it  can  be  imagined  that  starting  a  current  produces  a  stress 
which  strains  the  ether  or  stretches  it  in  one  direction;  stopping  it 
releases  the  strain.  Action  in  both  cases  starts  at  the  point  where  the 
current  is  produced  and  progresses  outward  with  the  speed  of  light,  and 
a  little  consideration  will  show  that  it  can  have  no  limit,  though  it  soon 
ceases  to  be  perceptible  except  under  certain  conditions,  to  be  later 
described. 

The  function  of  wireless  telegraphy  is  to  produce  these  ether  move- 
ments at  will. 

ELECTRIC   CAPACITY. 

44.  We  can  produce  momentary  currents  in  conductors,  whether  open 
or  closed,  by  the  cutting  of  lines  of  force,  and  the  evidences  of  electrifi- 
cation are  most  pronounced  at  the  ends  of  an  open  conductor,  but  these 

3 


34  MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

disappear  as  soon  as  the  cutting  of  lines  of  force  ceases.  We  find,  how- 
ever, that  electrification  of  amber,  glass,  silk,  and  other  bodies  remains 
after  the  rubbing  ceases.  We  can  produce  static  electricity  on  conduc- 
tors by  suitably  insulating  them.  For  instance,  if  two  metal  plates 
separated  by  a  piece  of  glass  are  connected,  one  to  the  positive,  and  the 
other  to  the  negative  pole  of  a  source  of  E.  M.  F.  and  then  simultaneously 
separated  from  it,  they  will  be  found  to  be  electrically  charged.  When 
two  plates  oppositely  charged  (art.  1)  are  connected  through  wires  lead- 
ing to  a  galvanometer,  the  amount  of  deflection  of  the  galvanometer 
needle  (caused  by  the  magnetic  field  of  the  momentary  current  created 
as  the  charges  unite  and  neutralize  each  other)  is  a  measure  of  the  quan- 
tity of  electricity  on  each  plate. 

In  testing  plates  of  different  sizes,  shapes,  and  materials,  charged  to 
the  same  potential  by  being  connected  to  the  poles  of  the  same  source 
of  electricity,  it  is  found  that  different  values  of  the  throw  of  the  gal- 
vanometer needle  are  produced.  Other  conditions  being  equal,  plates 
having  the  greatest  amount  of  surface  are  found  to  have  the  largest 
capacity/.  Plates  of  the  same  capacity  will  give  a  larger  throw  of  the 
galvanometer  when  charged  from  a  source  of  high  than  a  source  of  low 
potential,  so  that  the  amount  of  electricity  stored  in  an  electrified  body 
depends  on  its  potential  as  well  as  on  its  capacity. 


-  fl    + 


H|l|l|lh 


Fig.  22.  Fio.  22a. 

45.  If  two  plates,  oppositely  charged  by  being  connected  to  the  poles 
of  a  battery,  as  in  fig.  22,  or  to  the  terminals  of  a  dynamo  or  transfonner 
are  discharged  by  being  connected  through  a  galvanometer,  the  throw 
of  the  galvanometer  will  not  be  as  great  as  if  the  same  plates,  charged 
to  the  same  potential  by  the  same  battery  as  in  fig.  22a,  are  discharged 
through  the  same  galvanometer.  By  being  brought  closer  together  the 
plates  seem  to  have  their  capacity  increased.  It  takes  a  greater  amount 
of  electricity  to  bring  them  to  the  same  potential  than  when  farther 
apart.  If  two  plates,  charged  at  a  distance  from  each  other,  as  in  fig.  22, 
and  then  disconnected  from  the  battery  are  brought  to  the  position  shown 
in  fig.  22a,  their  potential,  as  measured  by  an  electroscope,  is  found  to 
be  lowered.  The  electricity  is  said  to  be  condensed  by  the  approach  of 
the  plates,  and  such  an  arrangement  is  termed  a  condenser,  a  somewhat 
misleading  term,  but  one  generally  used. 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  35 

This  is  analogous  to  the  increased  strength  of  magnetic  field  produced 
by  shortening  the  magnetic  circuit  while  retaining  tlie  same  magnetizing 
force.  In  both  cases  the  field  of  force  represents  stored  energy  which  can 
be  made  to  reappear  in  the  discharge  of  the  condenser  or  the  dissipation 
of  the  field. 

ELECTRIC  AND  MAGNETIC  INDUCTION. 

46.  Electric  lines  of  force  permeate  a  nonconductor — i.  e.,  electric 
induction  takes  place  through  it, — in  a  way  analogous  to  that  in  which 
magnetic  induction  takes  place  through  iron  or  air.     (See  note,  p.  18.) 

The  permeability  of  air  for  magnetic  induction  is  taken  as  a  standard 
and  called  unity.     (See  art.  25.) 

Its  permeability  for  electric  induction  is  also  taken  as  a  standard  and 
called  unity,  and  as  we  find  that  iron,  nickel,  cobalt,  and  oxygen  have  a 
greater  magnetic  permeability  than  air,  so  we  find  that  glass,  beeswax, 
paraffin,  nearly  all  kinds  of  oil,  and  indeed  most  bodies  we  call  insulators, 
have  a  greater  electric  permeability  than  air.  The  quality  of  a  body  as 
compared  with  air  in  this  respect  is  called  its  specific  inductive  capacity, 
and  bodies  when  considered  with  reference  to  electric  induction  through 
them  are  called  dielectrics.     (Art.  2.) 

It  is  found  that  the  best  quality  of  glass  has  nine  times  the  specific 
inductive  capacity  of  air.  This  means  that  when  subjected  to  the  same 
potential,  the  electric  field,  when  this  glass  is  the  dielectric,  is  nine  times 
as  strong  as  that  created  when  the  medium  intervening  between  the 
charges  is  air,  it  requires  nine  times  as  much  work  to  create  it,  and  its 
discharge  can  do  nine  times  as  much  work. 

47.  Bodies  such  as  iron  or  nickel  through  which  magnetic  induction 
is  taking  place  are  found  to  change  very  slightly  in  shape,  and  sudden 
changes  in  the  induction  or  lines  of  force  permeating  them  produce 
slight  sounds.  The  action  is  also  accompanied  by  the  production  of 
heat,  but  as  the  magnetizing  force  (magneto-motive  force)  increases, 
the  lines  of  force  tend  to  read  a  maximum  which  no  increase  of  mag- 
netizing force  will  increase.  When  in  this  condition  the  magnetized 
body  is  said  to  be  saturated.  There  is,  however,  apparently  no  limit  to 
the  magnetization  of  air. 

In  the  same  way  bodies  (dielectrics)  through  which  electric  induction 
is  taking  place  are  found  to  change  (enlarge)  slightly  in  shape,  but 
increase  of  electro-motive  force  (in  this  case  potential)  does  not  appear 
to  tend  to  a  maximum  of  electric  induction.  The  physical  strain  on  the 
dielectric,  however,  continues  to  increase  and  finally  reaches  a  point 
where  it  pierces  or  ruptures  the  dielectric,  the  action  being  accompanied 
by  a  sharp  crackling  sound  and  by  the  production  of  light  and  heat, 


36  MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 

which  we  call  an  electric  spark.  If  the  dielectric  is  air  or  a  liquid,  the 
rupture  is  immediately  repaired  by  the  action  of  the  surrounding  sub- 
stance on  that  heated  by  the  passage  of  the  spark ;  but  if  the  dielectric  is 
a  solid  the  rupture  is  permanent.  Magnetization  is  limited  by  satura- 
tion. The  limit  of  electrification  is  marked  by  rupture.  The  electric 
charges  are  found  to  have  been  dissipated  after  the  spark  has  passed. 
The  condenser  is  said  to  be  discharged.  If  the  oppositely  charged  plates 
are  discharged  without  sparking,  a  slight  sound  is  produced  if  the 
dielectric  is  glass.  This  is  analogous  to  the  minute  sounds  given  out  by 
magnets  when  magnetized  o^  demagnetized  suddenly. 

Magnetization  or  electrification  seems  to  consist  of  forcing  to  point  in 
the  same  direction,  like  magnetic  or  electric  polarities  of  the  molecules 
of  a  substance. 

ELECTRIC  CONDENSERS. 

48.  We  have  seen  that  the  capacity  of  an  electrified  body  depends  on  the 
area  of  its  electrified  surface,  on  the  nearness  of  its  charge  to  charges 
of  opposite  sign,  and  on  the  material  of  the  dielectric — i.  e,,  the  sub- 
stance intervening  between  the  charges. 

Bodies  capable  of  being  electrified  and  arranged  so  as  to  present 
a  large  capacity  in  a  small  space  are  frequently  called  simply  capacities, 
but  this  term  is  misleading,  and  though  the  term  condenser  is  not 
entirely  satisfactory  it  will  be  used.  The  total  charge  in  a  condenser 
depends  on  its  potential  as  well  as  its  capacity.  Its  potential  depends 
on  the  potential  of  the  source  of  electricity  only,  but  its  capacity,  as 
stated  above,  depends  on  its  size,  material,  and  arrangement. 

Condenser  capacities  may  be  said  to  be  related  to  each  other  in  the 
bame  way  as  rubber  bags  inflated  by  gas,  A  large  bag  charged  to  a 
given  pressure  contains  more  gas  than  a  small  bag  charged  to  the  same 
pressure.  The  gas  in  the  large  bag  is  making  no  greater  effort  to  escape 
per  square  inch  (i,  e.,  has  no  higher  potential)  than  the  gas  in  the 
small  bag;  but  it  requires  a  longer  time  and  more  gas  to  charge  the  large 
bag  than  the  small  one. 

So,  when  connected  to  the  same  source  of  electricity  it  requires  a 
longer  time  to  charge  a  condenser  of  large  capacity  to  a  given  potential 
than  it  does  to  charge  a  small  one  to  the  same  potential,  and  its  power 
to  do  work  is  correspondingly  greater. 

In  the  same  way,  it  requires  a  longer  time  to  create  the  magnetic  field 
of  a  large  electro-magnet  than  that  of  a  small  one,  and  a  stronger  mag- 
netic field  (within  limits)  is  created  by  a  large  current  than  by  a  small 
one  under  the  same  conditions,  and  the  energy  stored  in  the  strong  field 
and  its  power  to  do  work  is  correspondingly  greater. 


MANUAL    OF   RADIO    TELEGRAPHY    AND   TELEPHONY.  37 

49.  It  is  evident  that  a  close  analogy  can  be  drawn  between  the  electric 
field  in  a  condenser  and  the  magnetic  field  around  an  electrojimagnet. 
We  have  seen  that  any  movement  of  either  field  creates  the  other;  that 
they  can  exist  independently  only  in  a  static  condition ;  that,  though 
they  have  no  limits,  the  center  of  effort,  the  point  of  greatest  activity  in 
each,  is  at  the  body  which  we  consider  electrified  or  magnetized;  that 
bodies  differ  in  their  qualities  in  these  respects;  that  an  actual  physical 
change  takes  place  in  the  dielectric  when  electrified  and  in  the  iron  or 
nickel  when  magnetized,  and,  finally,  that  both  electric  and  magnetic 
fields  represent  stored  energy  in  an  infinitely  elastic  medium,  and  we 
shall  see  that  this  medium,  on  account  of  its  elasticity,  vibrates  and 
oscillates  when  either  an  electric  or  a  magnetic  field  is  suddenly  created 
or  destroyed  in  it. 

50.  The  most  common  and  best  known  form  of  condenser  is  the  Leyden 
jar,  which  consists  of  an  inner  and  outer  coating  or  film  of  tin  foil  or 
copper  on  a  glass  jar,  the  glass  being  the  dielectric.  Electric  induction 
takes  place  through  the  glass  and  the  energy  is  stored  in  the  electric  field, 
the  tin  foil  merely  serving  to  increase  the  area  over  which  electric 
induction  takes  place,  and  hence  the  rapacity  of  the  condenser. 

Fjaed  Condenser  Variable  Condenser 

Fig.  23.  Fig.  23a.  Fig.  23b. 

Condensers  are  often  made  up  of  a  large  number  of  interlaced  plates 
or  films  of  conducting  material,  having  between  them  for  a  dielectric 
larger  pieces  of  glass,  mica,  or  oiled  paper,  alternate  plates  being  simi- 
larly charged.  Condensers  are  represented  either  as  in  fig.  23  or  fig.  23a, 
They  will  be  represented  in  this  book  as  in  fig.  23.  Condensers  are  also 
made  in  which  the  relative  position  of  the  plates,  and  therefore  the 
capacity,  can  be  varied  at  will.  These  are  called  variable  condensers, 
and  will  be  represented  as  in  fig.  23b.  In  variable  condensers  the 
dielectric  may  be  glass,  air,  oil,  mica,  or  paper.  They  are  usually  made  of 
metal  plates  with  air  dielectric. 

DISCHARGE  OF  CONDENSERS. 

51.  If,  after  being  charged  by  connecting  the  inner  coating  to  one 
pole  of  a  source  of  electricity  and  the  outer  coating  to  the  other,  the  two 
coatings  are  connected  by  means  of  a  conducting  wire  the  charges 
neutralize  each  other  and  the  condenser  is  said  to  be  discharged.  The 
discharge  of  a  condenser,  being  a  movement  of  electricity,  creates  a  cur- 
rent and  consequently  a  magnetic  field  around  the  wire  through  which 
the  discharge  takes  place. 


38  MANUAL   OF    RADIO    TELEGRAniY    AND   TELEPHONY. 

If  the  potential  is  high  enough,  the  condenser  can  be  discharged  with- 
out acti|,ally  connecting  the  two  coatings,  for,  when  the  opposite  ends  of 
wires  connected  to  them  are  brought  within  a  certain  distance  of  each 
other,  sparks  will  pass,  and  the  condenser  will  be  found  to  be  discharged, 
the  same  as  if  the  wires  were  actually  connected.  The  charges  unite  by 
rupturing  the  air  dielectric.  Tlie  energy  stored  in  the  electric  field 
appears  as  sound,  light,  heat,  and  other  invisible  ether  vibrations. 

This  spark  discharge  is  found  when  analyzed  to  consist  usually  of 
several  sparks,  passing  first  in  one  direction,  then  in  the  other.  Each 
condenser  coating  is  charged  positively  and  negatively  in  rapid  succes- 
sion, each  charge  being  somewhat  less  than  the  preceding  until  the 
entire  energy  of  the  original  charge  is  dissipated.  This  form  of  con- 
denser discharge  is  oscillating.  The  released  charge  acts  like  a  released 
musical  string  which  vibrates  until  its  energy  is  dissipated,  and  as  the 
same  string  gives  out  the  same  note,  whether  stretched  strongly  or  only 
a  little,  so  a  condenser  when  discharged  through  the  same  wire  always 
vibrates  or  oscillates  in  the  same  period,  regardless  of  its  potential.  Just 
as  the  note  given  out  by  the  string  depends  on  its  material  and  length, 
so  the  rate  of  vibration  of  a  condenser  depends  on  its  capacity,  which,  as 
we  have  seen,  depends  on  its  material  and  arrangement. 

52.  Another  illustration  of  oscillatory  condenser  action  can  be  given: 
Let  fig.  24  represent  two  glass  vessels  connected  by  a  U  tube  with  a 
stopcock  at  the  bottom  of  the  tube.  One  vessel  is  filled  with  water  and 
the  other  empty.  If  the  U  tube  is  large  enough  to  permit  free  passage 
of  the  water,  when  the  stopcock  is  opened  quickly  the  pressure  in  the 
filled  vessel  will  cause  a  sudden  rush  of  water  up  the  other  side  of  the 
tube  into  the  empty  vessel,  which  will  continue  until  it  has  reached 
nearly  the  same  height  as  before  (fig.  24a) .  It  will  then  rush  back  into 
the  first  vessel,  and  so  on,  reaching  a  little  lower  level  each  time  until 
equilibrium  is  reached  at  the  same  level  in  both  vessels  (fig.  24b). 

The  only  action  which  prevents  the  oscillation  from  being  continuous 
is  friction  of  the  water  on  the  walls  of  the  tube  and  internal  friction 
between  its  molecules. 

Eeleased  condenser  charges  would  also  continue  to  oscillate  indefi- 
nitely if  it  were  not  for  the  resistance  in  the  discharging  wires  and  in 
the  dielectric  and  the  sound  and  light  produced  by  the  spark.  These 
absorb  the  energy  of  the  charge,  and,  being  relatively  large,  a  position 
of  equilibrium  is  reached  after  a  few  oscillations. 

If  the  U  tube  in  fig.  24  is  very  small  or  the  stopcock  only  slightly 
opened,  the  water  will  gradually  rise  on  the  other  side  and  will  finally 
reach  a  position  of  equilibrium  without  any  oscillation,  and  it  is  found 
that  if  the  condenser  discharge  takes  place  through  a  long  thin  wire, 
instead  of  a  thick  one,  the  condenser  is  slowly  discharged  through  it 
without  any  oscillation. 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY, 


39 


53.  The  oscillation  of  the  water  in  fig.  24  is  due  to  its  inertia.  Inertia 
is  a  property  of  all  bodies  and  is  in  amount  proportional  to  their  weight. 
It  is  represented  by  their  resistance  to  change  of  condition,  either  of 
motion  or  of  rest. 

The  water  in  the  first  vessel  falls  by  the  action  of  gravity/.  Once  in 
motion  its  inertia  (resistance  to  change  of  condition)  causes  it  to  rise 
on  the  opposite  side  against  the  action  of  gravity.  When  gravity  has 
overcome  its  inertia,  it  falls  again  by  gravity  and  is  carried  on  by  inertia. 


S  ^ 


Fig.  24. 


Fia.  24a. 


Fia.  24b. 

It  continues  to  overshoot  the  mark,  so  to  speak,  until  friction,  internal 
and  external,  brings  it  to  rest. 

Though  the  electric  charges  on  condenser  coatings  appear  to  be  inde- 
pendent of  gravity,  they  do  possess  inertia,  as  is  shown  by  their  resist- 
ance to  change  of  direction  and  by  their  oscillatory  movements. 

54.  Let  us  consider  a  charged  condenser  (fig.  25)  discharged  through 
a  thick  wire  connecting  the  coatings.  A  break  in  the  wire  prevents  the 
discharge  until  the  potential  is  high  enough  to  cause  sparks  to  cross  the 
break.  One  condenser  coating  before  discharge  is  at  a  certain  positive 
potential,  the  other  at  an  equal  negative  potential.  Both  discharge 
through  the  wire  in  the  same  time,  and  when  they  have  reached  zero 
potential  the  electric  field  has  been  dissipated,  but  the  moving  charges 


40 


MANBAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


in  the  wires  have  induced  a  magnetic  field  around  the  wire.  The 
strength  of  this  magnetic  field  depends  on  the  amount  of  the  moving 
charges,  i.  e.,  the  strength  of  the  current,  and  on  the  self-induction 
(art.  30)  of  the  wire  which,  as  we  know,  depends  on  its  shape  and  the 
material  (air  or  iron)  in  which  the  magnetic  field  is  created.  All  the 
energy  (except  that  lost  by  friction)  which  was  stored  in  the  electric 
field  is  now  in  the  magnetic  field  (fig.  25a).  The  magnetic  field,  having 
no  continuous  source  of  magneto-motive  force  (current)  to  maintain  it, 
collapses  on  the  wire,  producing  movements  of  the  electric  charges  into 
the  condenser  coatings,  which  now  become  charged  in  the  opposite  sense 
(fig.  35b).  The  electric  field  is  again  set  up,  containing  all  the  remain- 
ing energy,  and  the  magnetic  field  disappears  until  the  charges  again 
move  toward  each  other. 


OscjLiATiNa  Condenser  Discharge 


at  start  energy  all  electric. 
Fig.  25. 


end  of  quarter  cycle  energy 
all  magnetic. 

Fig.  25a. 


+ 

1  — 

^ 

; 

\ 

, 

—±» 

, 

tND  OF  HALr  CYcte 

energy  all  electric 
reversed. 

Fig.  25b. 


^r«  • — ^ 

fTEE-au/WTtfT  Cl 


€kd  or  TM 

energy  all  magnetic 
reversed. 

Fig.  25c. 


- 

1 

+ 

t+         - 

End  Of 

(Tycle 

energy  all  electric 
less  in  amount. 

Fig.  25d. 


The  attraction  of  the  unlike  charges  for  each  other  is  analogous  to 
the  attraction  of  gravity  for  the  water  in  fig.  24,  and  the  magnetic  field 
caused  by  the  self-induction  of  the  moving  charges  is  analogous  to  the 
inertia  of  the  water,  which  makes  it  rise  in  the  second  vessel,  because 
the  collapse  of  this  magnetic  field  charges  the  condenser  in  the  opposite 
sense,  and  for  this  reason  self-induction  is  sometimes  called  electro- 
magnetic inertia. 

From  the  foregoing  illustration  of  what  appears  to  take  place  during 
the  oscillating  discharge  of  a  condenser,  we  see  that  the  energy  before 
an  oscillation  begins  is  all  electric.  At  the  end  of  the  first  quarter  of  a 
cycle  it  is  all  magnetic.  At  the  end  of  a  half  cycle  it  is  all  electric,  but 
in  the  opposite  sense.  At  the  end  of  three-quarters  of  a  cycle  it  is  all 
magnetic,  but  with  the  direction  of  the  lines  of  force  reversed.  At  the 
end  of  a  complete  cycle  or  oscillation  the  energy  is  all  electric  again 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  41 

(figs.  25a,  25b,  25c,  25d)  and  in  the  original  sense,  but  less  in  amount 
on  account  of  the  losses  which  have  taken  place  during  the  transforma- 
tions and  which  are  shown  by  the  lieating  of  the  condenser  and  the  wires 
(and  the  sound  and  light  produced  by  the  spark  if  the  oscillations  take 
place  through  a  spark  gap).  At  all  intermediate  points  of  a  cycle  the 
energy  is  partly  electric  and  partly  magnetic. 

55.  A  complete  oscillation  or  cycle  is  made  up  of  two  alternations. 
The  highest  potential  reached  during  an  oscillation  is  called  the  ampli- 
tude of  the  oscillation.  The  difference  between  the  amplitude  of  two 
successive  oscillations  is  called  the  damping  and  is  a  measure  of  the 
losses.  The  interval  in  time  between  two  successive  oscillations  is  called 
the  period. 

56.  Since  every  body  has  electric  capacity  in  proportion  to  its  surface 
(art.  44),  and  since  movements  of  electric  charges,  without  which  9,  body 
can  not  be  electrified,  always  produce  magnetic  fields,  every  body  must 
have  self-induction,  and  therefore  electro-magnetic  oscillations  can  take 
place  in  it. 

We  know  that  every  body  vibrates  in  its  own  period  mechanically, 
and  we  find  that  every  body  vibrates  in  its  own  period  electrically,  and 
further  that  the  number  of  vibrations  or  oscillations  per  second  depends 
entirely  on  the  capacity  and  self-induction  of  the  body. 

It  will  be  seen  that  while  a  closed  circuit  is  necessary  for  the  flow  of 
a  continuous  or  direct  current,  for  oscillating  currents  a  straiglit  wire 
is  sufficient.  A  circuit  containing  a  condenser  which  would  completely 
obstruct  a  direct  current  has  no  effect  on  an  alternating  current  other 
than  to  change  its  sign. 

57.  We  must  be  careful  to  distinguish  between  the  capacity  of  a  con- 
denser and  the  total  charge  in  it,  and  between  the  self-induction  of 
a  wire  and  the  total  induction  caused  by  the  current  in  it.  The  capacity, 
it  may  be  repeated  again,  depends  on  the  material  and  arrangement  of 
the  charged  body.  The  total  charge — that  is,  the  total  electric  induction 
— depends  on  the  capacity  and  the  potential.  In  like  manner  the  self- 
induction  depends  on  the  arrangement  of  the  conductor  and  the  sur- 
rounding material  (whether  iron  or  air).  The  total  magnetic  induction 
depends  on  the  self-induction  and  the  current. 

58.  We  can  see  in  a  general  way  that  the  period  of  an  oscillating  circuit 
depends  on  the  capacity  and  self-induction  of  the  circuit,  and  not  on  the 
total  electric  or  total  magnetic  induction,  because  the  capacity  and  self- 
induction  are  determined  by  the  material  and  arrangement  of  the  circuit, 
which  qualities  determine  the  mechanical  period  of  a  body.  It  takes 
longer  to  discharge  a  condenser  of  large  capacity  than  one  of  small 
capacity,  and  it  takes  longer  to  create  a  given  current  in  a  circuit  of 
large  than  in  one  of  small  self-induction.    Increasing  the  potential  gives 


43 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


more  work  to  be  done  during  a  discharge,  but  also  gives  power  to  do  it 
in  the  same  ratio,  so  that  increase  of  potential  does  not  change  the  period, 
though  it  may  change  the  amplitude  of  the  oscillations. 

59.  It  was  stated  (art.  29)  that  coiling  a  wire  increases  its  self- 
induction  and  enables  a  strong  magnetic  field  to  be  created  around  it, 
and  that  this  increases  the  electrical  length  of  the  wire — i.  e.,  it  takes  an 
electrical  disturbance,  started  at  one  end  of  it,  longer  to  reach  the  other 
end  when  the  wire  is  coiled  than  when  the  same  wire  is  straight. 

Now  we  see  that  the  electrical  length  of  a  wire  depends  on  its  capacity 
and  self-induction  and  that  its  period  in  seconds — i.  e.,  the  time  of  one 
complete  oscillation  (the  time  required  for  an  electrical  impulse  started 
at  one  end  to  reach  the  other  and  be  reflected  back) — must  be  twice  its 
electrical  length  divided  by  the  distance  electricity  travels  in  a  second, 
which  we  know  to  be  the  same  as  light  (300,000,000  meters). 

The  capacity  and  inductance  of  a  straight  wire  long  in  proportion  to 
its  thickness  are  so  related  that  its  electrical  length  is  equal  to  its 
natural  length. 

From  the  above  the  period  or  time  of  one  complete  electrical  oscilla- 
tion of  a  straight  wire  one  meter  long  is  si^-uuioo-^  second,  and  it 
therefore  oscillates  150,000,000  times  per  second. 

The  number  of  oscillations  or  cycles  made  by  an  alternating  current 
per  second  is  called  its  frequency. 

60.  We  know  that  by  coiling  a  wire  its  self-induction  can  be  greatly 
increased,  and  its  period  thereby  lengthened.  By  adding  capacity  to  the 
wire  in  the  shape  of  condensers  its  period  can  be  lengthened  still  more, 
so  that  by  suitable  arrangements  a  circuit  having  small  mechanical 
length,  but  comparatively  great  electrical  length,  can  be  made  up  in  a 
small  space.* 


Pig.  26. 


-o     o- 

Fio.  26a. 


Such  a  circuit  is  shown  in  fig.  26.  It  is  made  up  of  a  condenser  con- 
nected to  a  coiled  wire,  and  will  be  called  in  this  book  an  oscillating 
circuit. 

*  It  must  not  be  forgotten  that  every  wire  possesses  capacity  by  virtue  of 
Its  surface,  and  self-induction  by  virtue  of  the  fact  that  an  electric  current 
can  flow  in  it.    Even  condensers  have  a  certain  amount  of  self-induction. 


MANUAL    OF    RADIO    TELEGRArilY    AND   TELEPHONY. 


43 


The  oscillating  circuit  in  fig.  26  may  have  a  break  or  gap  in  it,  as  in 
fig.  26a.  If  the  potential  of  the  condenser  is  sufficient  to  rupture  the 
air  or  other  dielectric  in  the  gap,  the  circuit  does  not  lose  its  oscillating 
character.  The  presence  of  the  gap  does,  however,  decrease  the  number 
of  oscillations  for  one  charge  and  prevents  the  complete  discharge  of  the 
condenser,  because  the  oscillations  cease  as  soon  as  the  potential  falls 
below  a  certain  value.  The  greater  the  loss  or  damping  in  each  oscilla- 
tion the  smaller  the  number  of  oscillations  that  will  take  place  before 
the  potential  falls  so  low  that  the  spark  ceases. 

61.  As  stated  in  art.  48,  the  term  condenser  is  not  satisfactory,  and 
the  word  capacity  is  often  used  to  mean  condenser,  especially  in  con- 
nection with  such  an  oscillating  circuit,  the  condenser  being  spoken  of  as 
a  capacitij  and  the  coiled  wire  as  an  inductance,  which  means  a  con- 
ducting wire  arranged  so  as  to  have  large  self-induction. 


-vQQQQQ^ 


-AAAA/^- 


Fig.  27.  Fig.  27a. 

Fig.  27. — Inductive  Resistance. 
Fig.  27a. — Noninductive  Resistance. 


Fig,  27  represents  an  inductive  resistance,  or  simply  an  inductance, 
since  it  is  assumed  that  all  wires  have  resistance. 

Fig.  27a  represents  a  noninductive  resistance,  or  simply  a  resistance — 
it  represents  a  coil  so  wound  that  the  currents  in  adjacent  turns  are  in 
opposite  directions  and  the  coil  has  therefore  no  self-induction. 

62.  An  oscillating  circuit  whose  electrical  length  can  be  varied  at  will 
is  represented  in  fig.  28.  It  consists  of  a  variable  condenser  in  connection 
with  a  fixed  inductance  (fig.  28),  or  it  may  consist  of  a  fixed  condenser 
and  a  variable  inductance  (fig.  28a),  or  both  capacity  and  inductance 


Fig.  28. 


Fig.  28a. 


may  be  variable,  the  arrow  in  fig.  28a  being  meant  to  show  that  any 
number  of  turns  of  the  coil  can  be  included  at  will. 

63.  Two  circuits  having  the  same  electrical  length  are  said  to  oscillate. 
in  resonance;  their  periods  are  equal,  though  the  inductance  and 
capacity  may  not  be  the  same  in  each. 


44 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


For  instance,  suppose  the  oscillating  circuit  (26a.)  is  adjacent  to  a 
wire,  as  in  fig.  28b,  having  the  same  electrical  length,  we  know  that  for 
oscillating  currents  (see  art.  56)  a  closed  circuit  is  not  necessary,  we 
also  know  that  by  reason  of  their  mutual  induction  (art.  15)  the  closed 
oscillating  circuit,  which  we  can  call  A  B,  will  induce  currents  in  the 
wire,  which  we  can  call  C  D.  Since  their  periods  are  equal  the  induced 
oscillating  current  in  C  D  will  be  suitably  timed  to  the  natural  period  of 
C  D  and  the  two  circuits  will  oscillate  in  resonance.  C  D  can  be  called 
the  open  circuit  as  distinguished  from  A  B,  the  closed  circuit. 


QroOnd 


Fig.  28b. 


Oscillating  circuits  now  used  in  wireless  telegraphy  have  electrical 
lengths  varying  from  100  to  5000  meters,  giving  from  1,500,000  to 
30,000  oscillations  per  second.  Those  first  used  by  Marconi  had  electrical 
lengths  of  about  6  centimeters  and  oscillated  approximately  2,500,000,000 
times  per  second. 

ETHER  WAVES. 

64.  As  stated  in  art.  55,  a  cycle  is  made  up  of  two  alternations  or  move- 
ments in  opposite  directions  and  can  be  represented  as  in  fig.  18.  Such 
a  curve  also  represents  the  crest,  hollow,  and  slope  of  regular  waves  on 
the  surface  of  the  ocean  or  other  body  of  water.  The  distance  from  crest 
to  crest  or  from  hollow  to  hollow  of  a  water  wave  is  called  a  wave  length, 
and  this  distance  is  equal  to  that  of  two  alternations.  Since  electro- 
magnetic (ether)  disturbances  spread  in  all  directions  with  the  speed  of 
light,  and  when  sent  out  by  an  oscillating  current  succeed  each  other  at 
equal  intervals  of  time,  and  since  the  magnetic  and  electric  forces  pro- 
duced by  oscillating  currents  change  direction  during  each  alternation, 
just  as  the  particles  of  water  rise  to  the  crest  or  fall  to  the  hollow  of  a 
wave,  their  positive  and  negative  amplitudes  may  represent  the  crests  and 
hollows  of  waves  separated  by  half  periods  or  half  wave  lengths,  an 


MANUAL   OF   RADIO    TELEGRAPHY    AND   TELEPHONY. 


45 


oscillating  current  may  be  called  a  wave  producer,  and  the  oscillations 
considered  as  movements  of  the  ether  may  be  called  ether  waves. 

65.  Hertz  (in  1886  at  Carlsruhe,  Germany)  was  the  first  to  show  that 
oscillating  electric  currents  really  do  produce  ether  waves — like  those  of 
light,  only  longer  and  subject  to  all  the  laws  governing  light  waves.  For 
this  reason,  wireless  is  sometimes  called  Hertzian  wave  telegraphy. 

66.  The  vibrations  of  particles  producing  sound  waves,  as  in  air,  con- 
sist of  to-and-fro  movements  parallel  to  the  direction  of  the  waves,  the 
latter  consisting  of  alternating  conditions  of  compression  and  rarefaction 
of  the  air. 

The  movement  of  the  particles  in  ether  waves  is  at  right  angles  to 
the  direction  of  propagation  of  the  wave,  and  the  electric  and  magnetic 
stresses  are  also  at  right  angles  to  each  other  at  any  point  in  the 
wave  front.  This  is  called  transversal  vibration,  as  distinguished  from 
the  longitudinal  vibration  of  the  particles  in  sound  waves. 


Fig.  18. 

When  one  particle  of  a  substance  is  displaced  or  made  to  vibrate,  it 
induces  its  neighbors  to  follow  it,  and  starts  them  to  vibrating  in  the 
same  periods  but  in  different  phases,  each  particle  starting  to  vibrate 
(passing  the  word,  so  to  speak)  at  a  definite  interval  of  time  after  the 
one  next  to  it  has  started.  The  vibrations  may  be  longitudinal  or  trans- 
verse, as  described  above,  or  they  may  be  circular  or  elliptical,  but  if  they 
are  regular  the  waves  produced  are  regular. 

The  amplitude  of  the  wave  (art.  55)  depends  on  the  extreme  limits 
from  its  normal  position  of  the  vibration  of  oacli  individual  particle. 
The  wave  length  depends  on  the  time  of  one  complete  vibration  of  each 
particle  and  the  velocity  with  which  the  displacement  or  vibration  is 
propagated  from  one  particle  to  another  of  the  substance.  Tt  is  found 
that  this  velocity  is  equal  to  the  square  root  of  the  elasticity  of  the  body 
divided  by  its  density. 

We  know  that  this  velocity  in  the  ether  is  300,000,000  meters  per 
second,  and  we  conclude  that  the  ether  must  have  very  great  elasticity 
combined  with  very  small  density. 


46  MANUAL    OF    KADIO    TELEGKAPIIY    AND    TLLEPPIONY. 

It  has  been  stated  that  electric  charges  or  electrons  are  the  only  things 
which  have  a  grip  on  the  ether,  and  that  when  they  are  vibrating  the 
ether  vibrates  with  them. 

When  a  particle  is  subject  to  several  forces  at  the  same  time,  it? 
resultant  movement  depends  on  the  resultant  of  the  forces  and  will  vary 
as  the  foices  vary,  so  that  a  body  can,  in  effect,  vibrate  in  more  than  one 
way  at  the  same  time,  and  can  produce  complex  waves  where  vibrations 
are  superimposed  on  each  other.  This  is  shown  every  day  at  sea  by  the 
small  waves  or  ripples  on  the  slopes  of  large  ones,  or  the  short  waves  from 
local  winds  superimposed  and  propagated  in  the  same  or  different 
directions  from  the  long  swells  due  to  distant  storms. 

67.  The  vibrations  producing  ether  waves,  and  consequently  the  wave 
lengths  and  frequencies,  are  of  an  almost  infinite  range,  for  instance: 

Ether  vibrations  from  430  to  740  trillions  per  second   (a  little  less 
than  one  octave)  are  visible  to  the  ej'^e  and  are  called  UgJit 
f      Between  870  to  1500  trillions  of  vibrations  per  second  we  have  the 
(    ultraviolet  and  X-rays,  and  from  430  down  to  300  trillions  of  vibrations 
j  per  second  what  are  called  infrarouge  rays. 

'*\      Below  300  and  down  to  20  trillions  of  vibrations  per  second  we  detect 

;  ether  vibrations  by  our  sense  of  feeling  or  by  the  thermometer,  and  they 

f    are  called  7iea^.  >  ..'^■'         ',    '   '    '  '  "« 

V      Twenty-five  octaves  lower  on  the  same  scale  are  the  ether  vibrations 

which  we  call  electric  waves  and  which  are  used  in  wireless  telegraphy. 

The  shortest  of  these  yet  measured  is  0.2  of  an  inch  in  length;  the 

longest,  over  1,000,000  miles. 

Marconi,  in  his  first  experiments,  used  a  pair  of  small  spark  balls 
which  gave  out  waves  about  12  centimeters  in  length. 

68.  Ether  waves  of  all  lengths  are  subject  to  reflection,  refraction, 
diffraction,  and  absorption,  and  bodies,  such  as  insulators  of  certain 
kinds,  which  are  opaque  to  the  short  waves  we  call  light,  are  transparent 
to  the  long  electric  waves  used  in  wireless  telegraphy.  Practically  all 
conductors  are  opaque  to  electric  waves.  Generally  speaking,  insulators 
are  transparent  to  electric  waves,  but  in  transmitting  the  wave  they 
absorb  some  of  its  energy. 

Conductors,  being  opaque  to  electric  waves,  partially  reflect  and  par- 
tially absorb  the  wave  energy. 

A  simple  case  of  wave  reflection  is  seen  when  a  rope  hanging  vertically 
is  given  a  quick  jerk  and  then  held  taut  in  the  hand.  A  wave  can  be 
seen  traveling  up  the  rope  till  it  reaches  the  top,  where  it  is  reflected, 
travels  down  the  rope  to  the  hand,  is  reflected  there  and  starts  up  again 
to  the  top,  and  so  continues  until  its  energy  is  damped  out. 

If  a  number  of  equally  timed  jerks  are  given,  a  succession  of  waves 
at  equal  intervals  is  sent  up  the  rope.    When  reflected  back  they  meet 


MANUAL    OF    RADIO    TELEGRAPHY    AND    TELEPHONY. 


47 


others  coming  up  whose  lengtlis  are  equal  to  those  coming  down.  At 
6ome  points  the  rope  tends  to  move  a  certain  distance  in  one  direction 
with  the  direct  wave,  and  the  same  distance  in  the  opposite  direction 
with  the  reflected  wave;  the  result  is  that  it  does  not  move  at  all. 
These  points  are  found  along  the  rope  one-half  wave  length  apart;  at 
all  other  points  the  rope  moves  or  vibrates  in  the  resultant  direction 
of  the  direct  and  reflected  wave  impulse,  and  what  are  called  stationary 
waves  are  set  up. 

The  points  at  which  there  is  no  movement  are  called  nodes,  and  points 
at  which  there  is  maximum  movement  are  called  loops.  This  is  shown 
graphically  in  fig.  18c. 


J^  V^fVC   LEMSTM 


3 
jt    WAVC    LtN«TH  —     -4*-!^  WAVE  LWeHHj 

Fig.  18c. 


Stationar}^  ether  waves  can  be  set  up  around  conducting  wires  by  suit- 
ably timed  electrical  impulses  applied  to  the  ends  of  the  wires. 

69.  It  will  be  observed  that  the  point  of  support  of  the  rope,  where  it 
can  not  move,  must,  in  every  case,  be  a  node.  So  in  a  conducting  wire, 
the  end  of  the  wire  away  from  that  receiving  the  impulses  must  be  a 
current  node,  because  no  current  can  flow  there.  It  can,  however,  and  a 
little  consideration  will  show  that  it  must,  be  a  potential  loop,  for  while 
there  is  no  movement  at  the  point  of  support,  the  greatest  pressure  or 
tendency  to  move  is  there. 


-fbrcNTiAi.  Loop 
JRRENT  Node 


R)TENTIAL  Loop- 
CURRCNT   Nooe- 


FiQ.  18d. 


Since  the  electrical  impulses  consist  of  variations  of  current  and 
potential,  which  succeed  each  other  regularly,  and  since  at  a  given  point 
we  find  a  loop  of  potential  and  a  node  of  current,  we  must,  at  a  quarter- 
wave  length  distant,  find  a  node  of  potential  and  a  loop  of  current. 

This  is  shown  graphically  in  fig.  18d,  which  represents  the  relative 
positions  of  current  and  potential  nodes  and  loops  in  stationary  electric 
waves,  and  illustrates  the  statements  made  in  art.  54  (figs.  25a,  etc.), 
relative  to  the  alternations  of  electric  and  magnetic  fields  in  oscillating 
condenser  discharges. 


48  MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

70.  If  an  oscillating  current  be  set  up  in  a  free  wire  (fig.  18e)  by  a 
neighboring  discharging  circuit  in  resonance  with  it,  the  free  wire  will 
be  found  by  measurement  with  a  micrometer  spark  gap  to  have  an  alter- 
nating potential  in  it,  varying  from  nothing  at  the  middle  point,  C,  to  a 
maximum  at  either  end  somewhat  similar  to  the  full  curve  EOF. 

If  at  the  same  time  the  current  in  the  free  wire  could  be  measured,  it 

would  be  found  to  have  a  maximum  value  at  C  and  a  minimum  at  the 

ends  similar  to  the  dotted  curve  A  D  B.     If  the  wire  A  C  B  is  not  too 

far  from  the  discharging  resonant  circuit  and  the  wire  be  cut  at  C  and 

E 


an  incandescent  lamp  L  be  connected  to  the  two  halves  as  shown  in  the 
figure,  the  lamp  Avill  glow. 

REFLECTION  OF  ETHER  WAVES. 

71.  If  ether  waves  impinge  on  a  reflecting  surface  not  normal  to  their 
direction,  they  are  reflected  at  an  angle  equal  to  that  which  the  reflecting 
surface  makes  with  their  original  direction  (the  angle  of  incidence  is 
equal  to  the  angle  of  reflection),  so  that  directed  waves  may  be  detected 
at  points  not  in  the  line  of  direction  by  the  interposition  of  a  reflector. 

Air  at  atmospheric  pressure  (about  760  millimeters  of  mercury)  is 
an  insulator.  Its  density  decreases  with  distance  above  the  earth's  sur- 
face, and  its  insulating  qualities  decrease  with  the  decrease  of  density. 
At  a  height  of  approximately  45  miles  above  the  earth's  surface  its  pres- 
sure is  about  1  millimeter  of  mercury.  At  the  density  corresponding  tc 
this  pressure  it  is  a  good  conductor,  and  though  still  transparent  to  short 
ether  waves  like  tliose  of  light,  it  partly  reflects  and  partly  absorbs  long 
ether  waves.  In  the  intermediate  distance  it  is  at  first  transparent,  then 
partially  transparent,  absorbent,  and  reflecting,  simultaneously. 

It  is  known  that  ether  waves  are  guided  by  conducting  surfaces  to  a 
certain  extent  (for  instance,  by  wires),  as  well  as  reflected  by  them,  and 
that  otherwise  they  travel  in  straight  lines.  Fig.  ISf  shows  the  approxi- 
mate path  of  an  ether  wave  started  from  the  earth's  surface  and  reflected 
from  the  upper  atmosphere.  It  will  be  seen  that  even  if  the  earth's 
surface  did  not  guide  the  waves  they  might  be  detected  at  points  below 
the  horizon. 

Other  causes  of  reflection  may  exist,  such  as  large  bodies  of  electrified 
air,  or  heavily  charged  clouds,  which  would  cause  interference  between 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  49 

direct  and  reflected  waves  and  make  electrical  shadows  at  certain  places, 
i.  e.,  points  at  which,  owing  to  conditions  outlined  above,  either  the 
waves  are  so  attenuated  that  they  can  not  be  detected  or  they  are  com- 
pletely neutralized. 


Fig.  18p. 
REFRACTION  OF  ETHER  WAVES. 

72.  When  ether  waves  impinge  on  transparent  bodies  at  any  angle 
other  than  the  normal,  if  their  velocity  in  the  transparent  body,  on 
account  of  its  elasticity  or  density,  is  different  from  that  at  which  they 
were  previously  moving,  that  part  of  the  wave  first  entering  the  body 
will  move  either  faster  or  slower  than  it  did  before.  The  part  outside 
will  therefore  either  fall  behind  or  gain  on  the  first  part.  This  action  will 
affect  each  portion  of  the  wave  front  as  it  enters  the  body,  and  the  result 
will  be  that  its  direction  of  movement  will  be  changed.  The  effect  is  to 
bend  the  wave  out  of  its  original  path,  and  the  action  is  called  refraction. 

Ether  waves  passing  through  the  atmosphere,  whose  density  varies  at 
different  points,  are  subject  to  this  bending  action.  The  bending  due  to 
refraction  tends  to  keep  the  wave  in  the  denser  atmosphere;  i.  e.,  it  is 
bent  towards  the  earth's  surface. 

DIFFRACTION   OF  ETHER   WAVES. 

73.  When  waves  meet  a  body  in  their  path  (for  instance,  when  the 
comparatively  long  waves  used  in  wireless  telegraphy  impinge  on  a  high 
island  or  mountain  range)  at  the  points  where  the  wave  front  cuts 
tlie  extreme  width  of  the  island  and  along  the  crest  or  summit,  new  cen- 
ters of  disturbance  are  created,  which  radiate  some  of  the  wave  energy  to 
points  behind  the  island  or  mountain.  It  has  the  effect  of  bending  the 
waves  around  the  object.  This  action  of  waves  is  called  diffraction.  In 
amount  it  depends  on  the  wave  length.  From  the  new  centers  of  disturb- 
ance waves  are  sent  out,  which  interfere  with  each  other,  not  being  propa- 
gated in  the  same  directions.  The  result  is  that  for  a  distance,  depending 
on  the  width  and  height  of  the  obstacle  and  on  the  wave  length,  a  shadow 
exists  beyond  it. 

Partial  reflection  of  the  waves  toward  their  source  takes  place  on  the 
side  of  the  obstacle  nearest  the  source.    An  attempt  to  show  this  graphi- 
4 


50 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


cally  is  made  in  fig.  18g,  but  the  best  illustration  is  given  by  the  motion 
of  water  around  a  rock  on  a  windy  day.  The  small  back  waves  on  the 
windward  side  are  reflected  to  windward.  The  waves  circling  or  bend- 
ing around  the  rock  are  diffracted.  The  still  water  in  the  lee  of  the  rock 
is  the  shadow,  in  which  no  action  exists.  At  a  distance  depending  on 
the  size  of  the  rock  and  the  wave  length  the  zones  of  interference  disap- 
pear, the  regular  waves  from  the  two  sides  of  the  rock  unite,  and  there 
is  no  evidence  of  its  existence  at  points  beyond,  though  it  has  decreased 
the  total  strength  of  the  waves. 


For  the  above  reasons,  high  land  between  two  wireless  telegraph 
stations  has  the  effect  of  decreasing  the  strength  of  signals  at  each 
station,  and,  if  close  to  either  station,  may  entirely  prevent  that  station 
from  receiving.  (It  may  be  in  the  shadow  or  be  subject  to  interference 
from  reflection.) 

The  effects  of  reflection  and  diffraction  on  waves  passing  over  irregular 
country  are  very  pronounced.  The  effects  of  reflection,  refraction,  and 
absorption  in  the  atmosphere  are  equally  pronounced,  the  qualities  of  the 
atmosphere  in  all  three  respects  varying  greatly  from  day  to  day  and 
between  day  and  night. 

An  ether  wave  traveling  from  one  wireless-telegraph  station  to  another 
over  rough  country  and  through  an  atmosphere  of  varying  density,  work- 
ing its  way  around  and  over  mountains,  being  balloted  from  thunder 
clouds  at  one  point  and  absorbed  by  semiconducting  gases  at  another, 
may  be  said  to  pursue  an  adventurous  journey. 


Chapter  II. 

PKODUCTION,  EADIATION  AND  DETECTION  OF 
ETHER  WAVES. 

74.  We  have  now  seen  how  to  produce  electric  and  magnetic  fields, 
how  to  utilize  magnetic  fields  for  the  production  of  electric  currents  in 
dynamos,  how  to  increase  the  potential  of  these  currents  by  means  of 
step-up  transformers,  and  how  by  means  of  this  high  potential  current 
to  force  large  charges  into  electric  accumulators  or  condensers  and  by 
discharging  these  condensers  in  oscillating  circuits  to  produce  what  we 
call  electric  or  ether  waves.  These  operations  can  be  represented  graphi- 
cally or  diagrammatically,  as  in  fig.  29,  which  shows  a  separately  excited 
A.  C.  dynamo  in  circuit  with  the  primary  winding  of  a  step-up  trans- 
former, whose  secondary  charges  the  condenser  of  an  oscillating  circvii 
containing  a  sparJc  gap. 


Fig.  29. 


The  secondary  winding  of  tlie  transformer  is  of  many  turns,  in  order 
to  give  a  high  potential.  The  transformer  also  has  an  iron  core.  The 
great  number  of  turns  of  the  secondary  winding,  added  to  the  effect 
produced  by  the  iron  core,  gives  the  circuit  containing  the  secondary 
winding  and  the  condenser  a  very  large  self-induction,  and  consequently 
a  very  long  period.  The  circuit  composed  of  the  condenser,  self-induc- 
tion, and  sparh  gap  has  a  very  much  shorter  period,  and  when  the  spark 
gap  is  ruptured  this  circuit  oscillates  as  if  it  were  entirely  disconnected 
from  the  secondary,  usually  completing  its  oscillations  and  coming  to  rest 
in  a  fraction  of  the  period  of  the  circuit  formed  ])y  the  secondary  and 
condenser. 

The  oscillating  circuit  (condenser,  spark  gap,  and  inductance)  is 
shown  in  fig.  29  near  a  conducting  wire,  having  a  few  turns  of  inductance 
close  to  those  of  the  oscillating  circuit.    In  this  circuit  we  can  consider 


52 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


Pig.  11. 


^LABY  ARCO 


TO  AEfflAU 
i 


the  condenser  as  representing  the  source  of  current,  like  the  battery  in 
fig.  11,  art.  13;  the  spark  gap  as  the  break  K,  the  turns  of  inductance 
in  the  oscillating  circuit  as  A  B,  and  the  open 
circuit  with  one  end  grounded  as  C  D.  The 
oscillating  currents  in  A  B  produce  like  cur- 
rents, but  in  the  opposite  direction  in  C  D  (art. 
12),  and  C  D  becomes  a  source  of  ether  waves. 
75.  The  production  of  ether  waves  and  their 
^^  detection  at  a  distance  from  the  source  constitute 

\^^^___^fe-=  ;£=;==- -"         wireless  telegraphy. 

1^     ^  U  C  D  is  usually  called  the  open  or  radiating 

circuit  or  aerial  circuit. 

A  B  the  closed  or  oscillating  circuit. 
The  two  inductances  in  A  B  and  C  D  form  the  primary  and  secondary, 
respectively,   of  an  air-core  oscillation   transformer    (art.   27).     When 
arranged  as  in  fig.  29,  A  B  and  C  D  are  said  to  be  inductively  connected. 
Or  C  D  may  have  part  of  its  inductance  common  to  A  B.  The  arrange- 
ment in  this  case  acts  as  an  auto-trans- 
former, and  the  circuits  are  said  to  be 
direct  connected  (fig.  29a). 

If  the  oscillating  and  radiating  cir- 
cuits have  the  same  period,  they  oscillate 
(      "  Or  or  vibrate  in  resonance.     The  radiating 

J    9  ^ks  circuit  in  such  a  case  receives  the  in- 

ductive impulses  from  the  oscillating 
circuit  at  the  proper  time,  and  the  am- 
plitude of  its  oscillations  is  thereby  in- 
creased. 

The  adjustment  of  A  B  and  C  D  to 
any  given  period  and  their  adjustment  to  each  other's  periods  is  called 
tuning. 

It  will  be  noted  that  tlie  oscillating  circuit  has  concentrated  capacity, 
while  the  capacity  of  the  radiating  circuit  is  distributed. 

76.  The  fundamental  principle  of  wireless  telegraphy  is  that  all  bodies 
vibrate  electrically  as  well  as  mechanically;  that  their  periods  of  electrical 
vibration  depend  solely  on  the  capacity  and  self-induction  of  the  vibrat- 
ing body;  that  these  electrical  vibrations  produce  ether  waves  which  are 
propagated  with  the  speed  of  light,  and  which  can  be  detected  at  great 
distances  from  their  source  by  means  of  instruments  specially  designed 
for  the  purpose. 

77.  Let  us  consider  a  little  more  closely  the  circuits  in  Fig.  29. 

First,  we  have  the  armature  windings,  the  leads  to  the  transformer  and 
the  primary  winding  of  the  transformer.  These  form  one  circuit  called 
the  primary  circuit. 


Fig.  29a. 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  53 

Second,  we  have  the  secondary  winding  of  the  transformer,  the  leads  to 
the  condenser  and  the  condenser.  These  form  a  second  circuit,  the 
secondary  circuit. 

Third,  we  have  the  condenser  and  leads,  the  spark  gap  and  leads  and  the 
closed-circnit  inductance.  These  form  a  third  circuit  called  the  clotzd 
circuit. 

Fourth,  we  have  the  open  circuit  inductance  and  the  leads  to  air  and 
ground,  forming  a  fourth  circuit  (for  oscillating  currents),  the  open 
circuit. 

There  is  also  a  fifth  circuit,  consisting  of  the  secondary  winding  of 
the  transformer,  the  closed  circuit  inductance,  spark  gap  and  leads.  This 
circuit  is  not  given  any  particular  name  and  only  becomes  of  interest  when 
the  spark  gap  remains  conducting,  after  having  once  broken  down. 

78.  As  has  been  stated  in  art.  74,  the  secondary  circuit  has  a  very  long 
period,  and,  for  the  same  reasons,  the  primary  circuit  has  likewise  a  very 
long  period,  compared  with  those  of  the  closed  and  open  circuits. 

If  the  design  is  such  that  the  primary  and  secondary  circuits  have  the 
same  period  they  are  found  to  operate  more  efficiently. 

79.  While  sending,  the  spark  gap  appears  to  be  sparking  continuously, 
but  it  is  really  sparking  a  very  small  percentage  of  the  time,  completing 
(as  has  been  stated)  its  oscillations  and  coming  to  rest  in  a  fraction  of  the 
period  of  the  secondary. 

If  the  spark  gap  were  in  operation  all  the  time  the  fifth  circuit  men- 
tioned above  would  short  circuit  the  transformer  through  the  gap  and  the 
closed  circuit  inductance  and  there  would  be  no  oscillation  and  no  electric 
waves  produced. 

When  this  condition  obtains,  what  is  called  an  arc  is  produced. 

An  arc  may  be  described  as  an  electrical  discharge  which  produces  light, 
heat  and  some  sound  and  is  a  continuous  rupture  of  the  dielectric,  as  com- 
pared with  a  spark  which  is  an  electrical  discharge  producing  light,  heat 
and  considerable  sound  and  which  is  intermittent  in  its  rupture  of  the 
dielectric. 

MUTUAL   INDUCTION   AND   COUPLING. 

80.  Let  us  now  endeavor  to  get  an  idea  of  how  energy  is  transferred 
from  one  circuit  to  another  until  it  reaches  the  open  circuit  and  is 
radiated  as  electric  waves. 

Referring  to  Fig.  29,  A  B  and  C  D  are  coupled  together  by  virtue  of 
their  mutual  induction  (art.  15).  The  induced  current  in  C  D  represents 
a  transfer  of  energy  from  one  circuit  to  the  other. 

If  their  mutual  induction  is  large,  the  circuits  are  said  to  have  close 
or  tight  coupling;  if  small,  the  coupling  is  said  to  be  loose. 

It  is  evident  that  the  mutual  induction  between  two  circuits  depends  on 
the  self-induction  of  each,  that  is,  the  strength  of  field  produced  by  vary- 
ing the  current  in  each  circuit.    Also,  that  it  depends  on  the  distance  apart 


54  MANUAL   OP   RADIO   TKLEGRAPHY   AND   TELEPHONY. 

of  the  two  circuits,  their  position  relative  to  each  other  (art.  22)  and  the 
material  (iron  or  air)  intervening. 

Mutual  induction  will  be  a  maximum  when  all  the  lines  of  force  created 
by  the  current  in  either  circuit  cut  the  other.  In  this  case  the  coupling 
is  said  to  be  perfect. 

If  the  two  circuits  are  moved  in  relation  to  each  other  so  that  only  part 
of  the  magnetic  field  of  each  cuts  the  other  circuit,  their  mutual  induc- 
tion is  decreased. 

The  mutual  induction  between  two  oscillating  circuits  alters  the  effec- 
tive self-induction  of  each,  making  it  apparently  larger  or  smaller  as  one 
circuit  is  receiving  energy  from  or  transferring  energy  to  the  other. 

81.  Since  the  natural  period  of  a  circuit  depends  on  its  self-induction, 
if  the  effective  self-induction  is  varied,  the  period  of  the  circuit  is  varied. 
Therefore,  coupled  circuits  having  the  same  or  nearly  the  same  natural 
periods  are  found  to  have  two  periods  of  oscillation,  one  faster  and  the 
other  slower  than  the  natural  period  of  each.  The  open  radiating  circuit 
generally  sends  out  electric  waves  of  two  lengths,  one  longer  and  one 
shorter  than  the  natural  wave  length  of  the  circuit.  The  closer  the  coup- 
ling the  greater  the  difference  in  length  of  these  two  waves.  This  differ- 
ence divided  by  the  natural  wave  length  of  the  circuits  is  called  the 
percentage  of  coupling.  For  instance,  if  an  open  circuit,  having  a  natural 
wave  length  of  400  meters,  sends,  when  coupled  to  a  closed  circuit  of  the 
same  natural  length,  two  waves,  one  of  445,  the  other  365  meters,  the 

,  .  T  445-365      oA«/ 

percentage  of  couplmg=  — ~— r —  =20%. 

82.  If  the  circuits  have  loose  coupling,  i.  e.,  are  moved  farther  apart, 
the  mutual  induction  is  less  and  the  difference  in  the  wave  lengths  radiated 
is  less.  This  distance  can  be  increased  until  the  two  waves  practically 
coincide  with  the  natural  wave  length  of  the  circuit.  This  is  very  loose 
coupling,  but,  since  without  mutual  induction,  no  energy  can  be  trans- 
ferred, the  two  can  never  be  the  same. 

Most  of  the  energy  is  found  to  be  in  the  longer  wave  and  until 
recently  that  in  the  short  wave  was  practically  wasted.  The  method  now 
used  of  generating  but  one  wave  length  will  be  described  in  art.  83. 

TRANSFER   OF   ENERGY   BETWEEN    COUPLED   CIRCUITS. 

83.  The  transfer  of  energy  between  coupled  circuits  having  the  same 
natural  period  is  well  illustrated  by  the  mutual  action  of  two  similar 
pendulums  connected  by  a  flexible  support.  If,  one  being  at  rest,  the 
other  is  pulled  aside  and  released,  the  swinging  pendulum  gives  properly 
timed  impulses  to  the  other  through  the  flexible  connection  and  starts 
it  to  swinging  also,  gradually  decreasing  its  owe  swings  while  the  other 
increases,  until  the  first  one  stops;  at  which  time  the  second  has  reached 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  55 

an  amplitude  nearly  as  great  as  that  of  the  first  swing  of  the  one  pulled 
aside.  In  other  words,  all  of  the  energy  has  been  transferred  to  the 
eecond  pendulum.  The  first  one  then  starts  again  and  increases  its 
swings  while  the  second  gradually  slows  down  and  comes  to  rest  at  which 
time  the  first  is  again  at  its  maximum.  All  the  energy  has  been  returned 
by  the  second  pendulum  to  the  first.  The  swings  are  slowly  damped 
by  air  friction  until  the  system  comes  to  rest.  If  the  periods  of  the  two 
pendulums  are  not  equal,  or  nearly  so,  the  impulses  are  out  of  step 
(resonance)  and  no  transfer  of  energy  takes  place — the  pendulum  first 
started  keeps  on  swinging  and  the  second  remains  at  rest. 

84.  If  the  points  of  support  by  the  flexible  connection  are  a  foot  or 
more  apart  (loose  coupling)  the  second  pendulum  picks  up  the  swing 
rather  slowly  and  both  pendulums  make  a  large  number  of  vibrations 
before  the  second  has  received  all  the  energy  from  the  first  and  the 
latter  has  come  to  rest. 

If  the  points  of  support  are  close  together  (close  coupling)  the  second 
pendulum  reaches  its  maximum  and  the  first  comes  to  rest  in  a  few  vibra- 
tions, the  transfer  of  energy  is  more  rapid,  and  the  damping  greater. 
The  ball  of  energy,  so  to  speak,  is  tossed  back  and  forth  between  them 
more  rapidly  than  when  they  are  farther  apart — more  loosely  coupled. 

Professor  Pierce  *  has  photographed  the  sparks  in  a  short  gap  in  the 
open  circuit  when  oscillating  in  connection  with  the  closed  circuit  and 
shows  that  they  occur  in  groups.  This  particular  circuit  showed  groups 
of  four.  In  other  words,  four  vibrations  sufficed  to  transfer  all  the 
energy  from  one  circuit  to  the  other. 

THE  QUENCHED  GAP.f 

85.  Having  once  transferred  all  of  the  energy  to  the  open  circuit,  we 
wish  to  radiate  it  and  not  have  any  retransfer  to  the  closed  circuit. 

What  is  called  a  "  quenched  gap  "f  has  the  advantage  of  stopping  the 
oscillations  of  the  closed  circuit  and  leaving  the  open  circuit  free  to  vibrate 
in  its  own  natural  period  and  it,  therefore,  radiates  waves  of  but  one 
length. 

86.  What  we  call  the  closed  circuit  is  only  closed  when  the  spark  gap 
is  conducting  and  its  period  in  that  condition  is  the  one  measured  either 
when  we  take  the  time  interval  between  sparks  or  determine  it  by  a  wave 
meter.  It  has  a  different  period  when  the  spark  gap  is  not  conducting 
because  its  capacity  with  reference  to  being  charged  from  the  open 
circuit  is  less  and  it  is  therefore  out  of  step  (art.  83)  with  the  open 

•  G.  W.  Pierce,  Principles  of  Wireless  Telegraphy,  1910,  p.  248. 

t  Discovered  by  N.  Wien  in  the  course  of  an  investigation  on  electrical 
discharges  between  metal  surfaces  placed  very  close  to  each  other,  and  pub- 
lished by  him  in  Oct.,  1906. 


56 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


circuit  and  the  latter  does  not  transfer  any  energy  to  it.  The  effect  of  the 
method  of  construction  of  the  quenched  gap  seems  to  be  to  restore  the 
nonconducting  character  of  the  gap  the  first  time  the  closed  circuit  comes 
to  rest,  and  thus  leave  the  open  circuit  free  to  radiate.  It  would  be  inter- 
esting to  take  photographs  in  both  circuits  to  determine  whether  this 
really  is  the  case. 

87.  Eeferring  to  art.  80  on  mutual  induction:  The  open  circuit  is 
first  set  to  oscillating  in  either  the  period  longer  or  shorter  than  its 
natural  period  and  has  reached  its  maximum  when  the  closed  circuit  has 


Fig.   18h. — Oscillations  from  Quenched  Spark-gap. 


stopped  and  opened.  Thereafter  the  open  circuit  is  free  to  vibrate  in  its 
own  period,  and  that  it  changes  to  that  period  can  be  shown  by  wave  meter 
readings,  but  in  building  up  it  is  sending  out  waves  of  a  different  period. 

The  first  maximum  reached  in  the  open  circuit  is  the  highest  maximum 
and,  since  no  further  loss  by  retransfer  to  the  closed  circuit  takes  place, 
the  quenched  gap  is  consequently  the  most  efficient.  It  will  also  con- 
duce to  efficiency  to  make  the  building  up  period  of  the  aerial  (when  it 
is  radiating  waves  of  a  different  length)  as  short  as  possible.  In  other 
words,  close  coupling,  but  close  coupling  increases  the  induced  E.  M.  F. 
in  the  condenser  circuit.  Therefore,  there  is  a  possibility  with  very  close 
coupling  of  retransfer  of  energy  by  breaking  down  the  gap  and  again 
closing  that  circuit. 

88.  We  can,  therefore,  conceive  of  a  wave  train  (art.  102)  from  an  ordi- 
nary open  circuit  as  made  up  of  a  series  of  waves  whose  amplitude  rises  and 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  57 

falls  during  the  transfer  and  retransfer  of  energy  from  one  circuit  to  the 
other;  the  rate  of  dying  away  depending  on  the  coupling  and  being  partly 
natural  (due  to  heating  and  radiated  energy  in  the  shape  of  electric 
waves),  partly  artificial  (due  to  retransfer  of  energy  to  the  closed  circuit) . 
A  wave  train  from  tlie  open  circuit  of  a  quenched  gap  can  be  repre- 
sented, as  in  fig.  62,  by  a  building  up  at  a  certain  frequency  (depending 
on  the  coupling)  to  a  maximum  depending  on  the  radiation  or  other 
losses  per  oscillation,  and  then  oscillations  in  the  natural  period  of  the 
open  circuit,  with  damping  dependent  on  the  radiation  and  resistance  of 
the  open  circuit  only.  The  closed  circuit  starting  at  a  maximum  and 
transferring  all  the  energy  to  the  open  circuit  in  a  few  oscillations  as 
shown  in  the  upper  part  of  fig.  18h;  there  being  no  retransfer  of  energy 
from  the  open  to  the  closed  circuit  and  vice  versa  as  occurs  with  the 
pendulums  discussed  in  arts.  83  and  84. 

METHODS  OF  PRODUCING  ELECTRIC  WAVES. 

89.  In  fig.  29a,  A  B  and  C  D  have  been  given  some  turns  in  common, 
forming  an  air  core-auto-transformer,  but,  whether  directly  or  inductively 
connected,  these  two  circuits — the  closed  and  open  circuits — must  have 
equal  natural  periods  in  order  to  produce  and  radiate  electric  waves 
efficiently. 

90.  We  can  omit  the  closed  circuit,  in  fig,  29,  and  excite  C  D  directly 
from  the  transformer  by  putting  a  spark  gap  in  C  D,  as  shown  in  fig.  29b. 

Since  C  D  has  some  capacity,  by  virtue  of  its  surface,  we  can  store  some 
energy  in  it  and  when  the  spark  gap  breaks  down,  this  energy  will  oscillate 
in  C  D  as  an  electric  current  and  will  produce  electric  waves.  This  is  one 
of  the  earliest  methods  of  producing  electric  waves  for  wireless  telegraphy 
and  was  usually  called  plain  aerial,  C  D  being  known  as  the  air  wire  now 
called  aerial  or  antenna. 

91.  Arrangements  for  producing  electric  waves  may  be  simplified  still 
more  by  dispensing  with  the  transformer  and  connecting  the  alternator 
terminals  directly  across  the  gap.  The  transformer  is  only  used  to  increase 
the  potential  of  the  condenser  or  aerial  and,  therefore,  store  up  more 
energy  between  discharges  and  produce  oscillations  of  greater  amplitude. 
If  we  could  conveniently  generate  a  high  potential  directly  in  the  alter- 
nator, the  transformer  would  not  be  used. 

92.  Many  attempts  have  been  made  to  do  this,  the  most  successful  being 
when  the  oscillations  are  generated  directly  in  the  dynamo  and  C  D  is  con- 
nected directly  to  its  terminals,  as  in  fig.  29c.  In  this  case  the  armature  of 
the  alternator  is  stationary  and  consists  of  one  or  more  turns  of  wire  around 
each  of  a  large  number  of  stationary  poles,  past  which  the  field  poles  are 
moved  at  very  high  speeds  and  the  natural  frequency  of  the  aerial  (CD), 
combined  with  the  armature  winding,  is  the  same  as  the  alternator 
frequency. 


58 


MANUAL    OF    RADIO    TELEGiiAPHY   AND   TELEPHONY. 


SOO  TO   lOOO    VOl_TS    DC 


FiQ.   29e. 


MANUAL   OF    RADIO    TELEGRAPHY    AND    TELEPHONY.  59 

It  will  be  seen  that  the  oscillations  thus  produced  and,  therefore,  the 
waves  radiated,  are  continuous  and  not  intermittent  as  when  a  spark  gap 
is  used. 

C  D  may  have  but  a  small  capacity,  but  it  receives  a  charge  at  everj 
oscillation,  instead  of  being  intermittently  charged  and  allowed  to  dis- 
charge gradually. 

However,  in  order  to  produce  wave  lengths,  say  of  3000  meters,  the  field 
revolutions  and  numbers  of  poles  must  be  such  as  to  produce  a  frequency 
of  100,000  cycles  per  second.    This  involves  great  mechanical  difficulties. 

E.  A.  Fessenden  and  E.  F.  W.  Alexanderson  have  designed  such  genera- 
tors, turning  at  more  than  300  revolutions  per  second,  but  they  have 
not  yet  become  commercially  successful. 

Machines  are  now  built  to  produce  high  frequency  with  lower  mechani- 
cal speeds  by  special  windings  of  fields  and  armatures  or  transformers, 
but  such  apparatus  is  not  yet  in  general  use.* 

93.  As  has  been  indicated  in  figs.  11a  and  lib,  oscillations  can  be  pro- 
duced by  suddenly  making  and  breaking  direct  current,  with  or  without 
an  induction  coil  (transformer)  intervening,  and  some  very  large  inter- 
rupted current  sets  have  been  built  and  are,  or  have  been,  used  for  trans- 
atlantic wireless  telegraphy  by  Mr.  Marconi. 

94.  Even  before  wireless  telegraphy  existed,  it  was  known  that  an  arc 
produced  by  direct  current  would  produce  electrical  oscillations  if  in 
circuit  with  an  inductance  and  a  condenser,  and  that  these  oscillations 
were  produced  continuously  if  the  circuit  was  adjusted  properly. 

This,  known  as  the  arc,  as  contrasted  with  the  spark  method,  of  produc- 
ing electric  waves,  is  illustrated  in  figs.  29d  and  29e. 

It  will  be  observed  that  the  only  difference  between  fig.  29d  and  fig.  29 
is  that  we  have  direct  instead  of  alternating  current  and  the  arc  instead  of 
the  spark  gap. 

It  is  found  also  that  the  arc  can  be  made  to  produce  oscillations,  if 
mounted  as  in  fig.  29e,  i.  e.,  directly  in  the  aerial,  and  that  it  operates  better 
if  placed  in  a  very  powerful  magnetic  field,  as  shown  in  fig.  29e,  and  oper- 
ated at  a  high  potential,  in  a  heat  conducting  atmosphere,  such  as  a  gas 
largely  composed  of  hydrogen. 

95.  We  see,  therefore,  that  we  can  and  do  produce  both  intermittent 
and  continuous  electric  oscillations,  with  alternating  current  and  also  with 
direct  current. 

Continuous  or  undamped  oscillations  are,  generally  speaking,  produced 
without  noise  and  radiated  at»  lower  potentials  than  intermittent  ones. 
Other  advantages  of  continuous  oscillations  will  appear  later.  As  yet  they 
are  not  in  general  use  and  are  somewhat  more  difficult  to  regulate  than 
intermittent  oscillations. 

*  Professor  Rudolph  Goldschmidt  and  Count  Arco  have  designed  and  con- 
Btructed  such  machines. 


60 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


RADIATION  OF  ELECTRIC  WAVES. 

96.  It  has  been  stated  that  every  oscillating  circuit  must  contain 
inductance  and  capacity.  This  is  true  even  though  the  circuit  consists  of 
straight  wires,  for  these  have  distributed  inductance  and  capacity.  If 
the  circuit  is  formed  as  in  fig.  26a  with  a  coil  of  wire  and  a  condenser, 
the  inductance  and  capacity  are  said  to  be  concentrated  or  lumped.  There 
is  also  a  certain  amount  of  distributed  inductance  and  capacity,  but  in 
general  this  will  be  small  compared  with  the  concentrated  portions. 

In  the  case  of  a  linear  oscillator  (fig.  30),  when  the  oscillations  are 
taking  place  and  the  charges  are  most  widely  separated,  we  may  imagine 
lines  of  electric  force  to  be  connecting  each  unit  of  positive  electricity  on 
one  end  to  a  unit  of  negative  electricity  on  the  other.  For  clearness  of 
conception  we  may  picture  these  lines  of  force  as  having  a  real  exist- 


,  »  >  >  i 

1  1  1  '  1 

■  I  I  "  I 

9.'  ;  •'  !  I  j 


Fig,  26a. 


\    \    \ 


I     I 
I     I 


/ 


Fig.  30. 


Fig.  31. 


Fig.  26a. — Non-radiating  Circuit. 

Fig.  30. — Radiating  Circuit. 

Fig.  31. — Electric  Wave  Leaving  Oscillator. 


ence  and  exerting  an  elastic  pull  between  the  positive  and  negative  units, 
tending  to  draw  them  together,  while  at  the  same  time,  provided  they 
are  running  in  the  same  direction,  they  tend  to  repel  each  other.  These 
lines  of  force,  in  the  case  of  a  linear  oscillator,  on  account  of  their 
repulsion  away  from  the  oscillator,  form  wide  loops  which  tend  to  snap 
off  and  travel  away  into  space  when  the  charges  again  rush  back  through 
the  spark  gap,  thus  forming  electrical  waves  or  radiation  as  shown  in 
fig.  31.  In  the  case  of  the  circuit  shown' in  fig,  26a,  where  the  principal 
capacity  lies  in  the  condenser,  the  lines  of  force  are  concentrated  between 
the  condenser  plates.  They  do  not  loop  out  to  any  extent,  and  hence 
such  a  circuit  radiates  very  feebly.  On  account  of  these  differences  an 
open  circuit  oscillator  (fig.  30)  is  often  called  a  radiating  circuit,  while 


MANUAL    OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


61 


a  closed  circuit  (fig.  26a)  is  called  non-radiating,  although  all  high 
frequency  circuits  radiate  in  some  degree. 

97.  Let  fig.  32  represent  a  closed  circuit  inductively  connected  to  a 
vertical,  grounded,  open  circuit  or  aerial,  and  suppose  the  spark  gap  to 
break  down  at  the  point  of  maximum  potential  of  the  charging  current. 
At  this  instant  there  is  no  current  in  the  closed  circuit  and,  therefore, 
no  current  in  the  open  circuit.  The  energy  is  all  electro-static,  all  in  the 
closed  circuit  and  practically  all  in  the  electro-static  field  between  the 
condenser  plates,  the  capacity  of  the  spark  points  and  other  parts  of  the 
circuit  being  very  small. 

As  soon  as  discharge  through  the  spark  gap  commences,  the  field  of  the 
current  in  the  closed  circuit  inductance  induces  movements  of  electric 


+  u- 


J 
1 


Fig.  32. 


Fig.  32a. 


charges  in  the  open  circuit,  the  starting  point  of  the  disturbance  being 
the  open  circuit  inductance.  As  the  charges  in  the  open  circuit  separate, 
they  are  connected  by  electro-static  lines  of  force  and  surrounded  by 
magnetic  lines  of  force,  both  moving  outward  at  the  same  rate  that  the 
charges  move  in  a  straight  wire. 

The  electro-static  field  becomes  a  maximum  when  the  charge  reaches 
the  top  of  the  wire.  At  this  time  the  magnetic  field  is  a  minimum.  At 
the  expiration  of  a  half  period,  when  the  charges  meet  again,  the  mag- 
netic field  is  a  maximum,  but  reversed  in  direction.  The  electro-static 
field  reverses  as  the  charges  separate  again.  If  they  can  be  represented 
as  meeting  in  the  open  circuit  inductance,  the  electro-static  field  just  after 
the  end  of  a  half  period  can  be  represented  as  in  fig.  32a,  where  the 
mutual  repulsion  of  the  electro-static  lines  of  force  outside  the  wire  has 
kept  them  from  returning  as  fast  as  the  charges  travel  towards  each 


62  MANUAL    OF    RADIO    TELKGRAPIIY    AND   TELEPHONY. 

other.  As  the  charges  meet,  the  ends  of  the  lines  of  electric  force  unite 
and  become  closed  circuits,  or  electric  whorls  shaped  like  smoke  rings 
which,  owing  to  the  mutual  repulsion  of  all  their  parts,  expand  outward, 
upward,  and  downward. 

It  is  in  some  such  manner  that  we  can  conceive  energy  to  be  detached 
and  sent  out  into  space  from  wires  forming  oscillating  circuits. 

The  expanding  rings  touch  the  earth  and  are  guided  by  it  as  by  any 
other  conductor,  thus  resembling,  near  the  earth,  expanding  hemispherical 
shells. 

These  may  be  called  earthed  waves  to  distinguish  them  from  the  free 
waves  which  exist  momentarily  in  the  vicinity  of  an  ungrounded 
oscillator  (fig.  31). 

98.  If  the  point  of  connection  with  the  closed  circuit  is  considered 
as  at  the  earth,  earthed  waves  only  are  generated  and  detached  from  the 
aerial  and  no  free  waves  exist  at  any  time.  The  production  of  earthed 
electric  waves  under  these  conditions  is  illustrated  in  fig.  33. 


•':S>>/'\  .-/>\  ''\; 


Fig.  33. — Earthed  Electric  Waves. 

We  know  that  earthed  waves  are  guided  by  conducting  surfaces;  we 
know  that  light  waves  are  not;  we  do  not  know  where  the  dividing  line 
is  between  waves  that  are  radiated  in  straight  lines  and  those  that  are 
guided  by  conductors. 

99.  For  simplicity,  we  have  described  the  process  of  radiation  in  terms 
of  electro-static  lines  of  force,  but  it  must  not  be  forgotten  that  a  moving 
electro-static  field  always  produces  a  magnetic  field  at  right  angles  to 
itself  and  at  right  angles  to  the  direction  of  movement,  so  that  we  have 
electro-static  lines  perpendicular  to  the  surface  of  the  earth  (at  least  near 
the  aerial),  and  magnetic  lines  in  circles  surrounding  the  aerial. 

Both  the  electro-static  and  the  electro-magnetic  fields  reverse  their 
directions  every  half  wave  length. 

The  process  of  radiation  withdraws  energy  from  the  circuit  just  as  is 
the  case  when  a  resistance  is  placed  in  the  circuit;  hence  radiation 
resistance  is  an  expression  often  used,  meaning  the  resistance  which  under 
the  given  conditions  would  use  up  the  same  amount  of  energy  as  that 
removed  from  the  circuit  by  radiation.    This  radiation  resistance  depends 


MANUAL   OF    RADIO    TELEGKAl'IIY    AND   TELEPHONY.  63 

only  on  the  form  and  dimensions  of  the  aerial  and  on  the  frequency  of 
the  oscillations,  increasing  rapidly  as  the  frequency  increases.  It  is 
independent  of  the  intensity  of  the  oscillations  and  of  other  sources  of 
lost  energy  in  the  circuit. 

Eadiation  resistance  might  be  called  the  radiation  coefficient.  Accurate 
means  of  measuring  it  are  not  yet  in  general  use. 

DAMPED  OSCILLATIONS. 

100.  It  has  been  explained  (art.  54)  that  when  a  circuit  consisting  of 
a  condenser,  inductance,  and  spark  gap  is  charged  by  a  transformer  to  a 
potential  so  great  that  a  spark  passes  across  the  gap,  the  electricity  stored 
up  in  the  condenser  discharges  itself  through  the  spark  gap,  and  by  its 
inertia  charges  the  condenser  in  the  opposite  sense,  only  at  the  next 
instant  to  again  discharge  itself,  and  so  on.  All  this  takes  place  during 
the  time  of  one  spark,  and  in  fact  this  surging  of  electricity  is  what  keeps 
the  spark  in  existence  after  the  first  discharge.  This  surging  back  and 
forth  would  continue  indefinitely  were  it  not  for  the  energy  used  up  in 


Fia.  34. — Damped  Oscillations.    Energy  Supplied  at  Beginning  of  Wave-train. 


tlie  heat  of  the  spark  and  in  the  resistance  and  other  losses  in  the  rest 
of  the  circuit.  But  as  no  new  energy  can  be  introduced  into  the  circuit 
until  the  condenser  is  recharged,  the  electrical  surgings  decrease  in 
intensity  and  finally  cease. 

If  we  represent  time  by  the  horizontal  axis  and  the  amplitude  of  the 
oscillations  by  the  vertical  axis,  fig.  34  will  show  graphically  the  course 
of  the  phenomenon.  It  is  exactly  analogous  to  a  light  pendulum  which 
is  set  swinging  and  which  is  brought  to  rest  after  a  limited  number  of 
swings  by  the  friction  of  the  air. 

Gradually  decreasing  oscillations  of  this  kind  are  called  damped  oscil- 
lations and  obey  the  law  that  each  succeeding  amplitude  is  a  given 
fraction  of  the  one  before  it. 

UNDAMPED    OSCILLATIONS. 

101.  It  has  been  seen  in  the  last  article  that  the  cause  of  the  dying 
out  of  a  train  of  oscillations  in  a  spark  circuit  is  the  using  up  of  energy 
in  the  circuit  together  with  the  fact  that  no  energ}'  can  be  brought  in 
from  outside  to  compensate  this  loss.    If  means  can  be  found  for  keeping 


64  MANUAL    OF    RADIO    TELEGRAPHY    AND    TELEPHONY. 

up  a  constant  supply  of  energy,  such  as  an  alternator  directly  connected 
to  the  aerial  or  an  arc  transmitter,  our  oscillations  can  be  made  to  continue 
indefinitely  and  with  equal  amplitude  as  in  fig.  35. 


Fia.  35. — Undamped  Oscillations.    Energy  Constantly  Supplied. 

102.  The  electric  waves  radiated  during  one  set  of  oscillations  are 
called  a  wave  train.  If  more  than  one,  the  wave  trains  radiated  during 
one-half  cycle  of  the  charging  current  are  called  a  group  of  wave  trains. 

The  duration  of  a  wave  train  is  the  time  of  one  oscillation  multiplied 
by  the  number  of  oscillations  in  the  train. 

It  is  found  that  the  duration  of  a  wave  train  is  much  less  when  the 
oscillating  circuit  (A,  B,  fig.  29)  is  connected  to  an  aerial  with  one 
end  free  and  the  other  earthed,  like  C  D,  than  when  it  oscillates  without 
any  other  electrical  connection.  The  energy  is  radiated  more  rapidly,  the 
vibrations  more  quickly  damped.  It  is  for  this  reason  that  the  circuit 
formed  by  the  condenser,  spark  gap,  and  inductance  is  called  the  closed  or 
oscillating  circuit;  that  formed  by  the  aerial,  inductance  and  ground,  the 
open  or  radiating  circuit.    (See  art.  75.) 

103.  Considering  the  series  of  expanding  hemispherical  shells  referred 
to  in  art.  97,  and  shown  in  fig.  33,  if  there  is  but  one  wave  train  per 
alternation  of  the  condenser  charging  current,  the  thickness  of  one  of 
these  series  is  equal  to  the  wave  length  multiplied  by  the  number  of  oscil- 
lations per  train.  Suppose  this  to  be  10  and  the  wave  lengths  500  meters, 
then  the  depth  of  a  wave  train  is  5000  meters,  or  a  little  more  than  three 
miles.  If  the  frequency  of  the  alternating  current  is  60  cycles,  or  120 
alternations  per  second,  we  have  120  wave  trains  per  second,  and  since 
they  travel  at  the  rate  of  186,000  miles  per  second  the  wave  trains  have 
intervals  of  1550  miles  between  them,  so  that  M'Orking  at  ordinary  dis- 
tances and  at  this  frequency,  each  wave  train  has  passed  the  receiving 
station  before  its  successor  has  left  the  sending  station. 

If  the  alternator  frequency  is  500,  the  wave  trains  are  only  186  miles 
apart,  or  about  the  distance  of  ordinary  daylight  communication  between 
ships. 

104.  When  the  spark  gap  is  set  to  break  down  at  the  maximum  charg- 
ing potential,  the  condenser  absorbs  and  stores  all  the  energy  that  can  be 
transferred  by  the  charging  transformer  during  an  alternation.  When 
it  discharges,  it  transfers  part*  of  the  energy  to  the  open  circuit  to  be 

♦  Experimentation  has  proven  that  from  80  to  90  per  cent  of  the  energy 
delivered  to  the  transformer  is  transferred  to  the  spark  circuit. 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


65 


radiated  as  electric  waves.  Since  its  period  of  discharge  is  very  short 
as  compared  with  that  of  the  cliarging  current  the  latter  current  does  not 
appreciably  change  during  the  time  the  condenser  is  discharging.  This 
current  immediately  begins  to  again  charge  the  condenser,  but  the  poten- 
tial of  the  latter  does  not  rise  high  enough  to  cross  the  gap  so  that  the  con- 
denser soon  begins  to  return  energy  to  the  charging  circuit.  It  does 
this  until  its  potential  and  the  charging  potential  (and  current  if  they 
are  in  phase)  falls  to  zero.  It  then  begins  to  absorb  energy  again  with  the 
reverse  potential,  and  on  reaching  the  maximum  again  discharges  across 
the  gap. 

Fig.  36  is  an  attempt  to  illustrate  this  action  graphically.  The  area 
included  by  the  curve  on  the  left  of  the  zig-zag  line  indicates  the  work 


Fig.  36. 


done  on  the  condenser  during  the  first  half  of  an  alternation;  the  zig- 
zag line  indicates  the  number  and  amplitude  of  vibrations  made  by 
the  closed  circuit  in  transferring  the  energy  to  the  radiating  circuit. 
The  area  included  by  the  curve  on  the  right  of  the  zig-zag  line  repre- 
sents the  work  done  during  the  second  half  of  the  alternation  in  recharg- 
ing the  condenser.     This  work  is  all  returned  to  the  charginor  circuit. 


DECREASE  OF  AMPLITUDE  WITH  DISTANCE  FROM  SOURCE. 

105.  From  the  discussion  in  art.  103  on  the  thickness  of  the  hemi- 
spherical shell  enclosing  a  train  of  ether  waves,  if  we  assume  this  thick- 
ness to  remain  constant  and  that  part  of  the  shell  near  the  earth  to  be 
represented  by  an  expanding  cylinder,  it  is  increasing  in  size  by  one 
dimension  only,  viz.,  circumference,  and  therefore  the  energy  in  any  part 
of  this  shell  will  vary  inversely  as  the  distance,  instead  of  inversely  as  the 


66  MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

square  or  cube  of  the  distance  from  the  source,  as  would  be  the  case  if 
expansion  were  taking  place  in  two  or  in  three  directions. 

But  it  appears  that  expansion  takes  place  in  two  directions;  since 
Messrs.  W.  Duddell  and  J.  W.  Taylor,  in  experiments  made  for  the 
English  Navy  in  1905,  proved  that  (at  least  for  distances  up  to  60  miles) 
the  received  ciirrent  as  stated  above  varies  inversely  as  the  distance  from 
the  sending  station,  and  the  received  energy  varies  inversely  as  the  square 
of  the  distance.  But  additional  experiments  by  Dr.  L.  W.  Austin  show 
that  this  law  does  not  hold  except  for  very  short  distances,  and  that  the 
amplitude  is  lessened  from  other  causes  than  those  due  to  distance  alone. 
We  loiow  that  the  energy  is  absorbed  in  the  atmosphere  more  by  day- 
light than  by  night — more  at  high  (summer)  than  at  low  (winter)  tem- 
peratures. The  amount  of  absorption  as  between  one  day  and  another 
probably  depends  also  on  the  electric  condition  of  the  atmosphere. 
Long  waves  suffer  less  absorption  than  short  ones.  Irregular  country 
produces  large  absorption.  The  absorption  over  some  soils  is  for  com- 
paratively long  distances,  30  times  as  great  as  over  sea  water.  Trans- 
mission over  salt  water  is  the  best. 

106.  As  illustrating  the  difference  in  absorption  between  short  and  long 
waves,  the  greater  efficiency  of  short  waves  for  short  distances,  and  the 
rapid  falling  off  at  distances  above  100  miles.  Dr.  Austin  finds :  Strength 
of  received  signals  at  20  miles,  using  300  meter  waves,  5  times  as  great 
as  with  1500  meter  waves;  at  100  miles,  4  times  as  great  as  with  1500 
meter  waves;  at  400  miles,  1.6  times  as  great  as  with  1500  meter  waves; 
at  800  miles,  signals  from  300  meter  waves  weaker  than  from  1500  meter 
waves. 

Using  300  meter  waves,  he  finds,  strength  of  signals  at  200  miles,  0.3  of 
that  at  100  miles;  at  400  miles,  0.053  of  that  at  100  miles;  at  800  miles, 
0.0036  of  that  at  100  miles.     (See  table  11,  appendix  A.) 

DETECTION  OF  ELECTRIC   WAVES. 

107.  We  believe  that,  generally,  the  direction  of  the  magnetic  lines  of 
force  at  any  point  in  a  wave  near  the  earth  is  parallel  to  the  earth's  sur- 
face and  at  right  angles  to  a  line  joining  the  point  with  the  source  of  radia- 
tion; and  that  the  direction  of  the  electro-static  lines  of  force  at  any  point 
near  the  earth  is  perpendicular  to  the  earth's  surface. 

An  iron  wire  placed  horizontally  and  parallel  to  the  lines  of  magnetic 
force  will  be  magnetized  by  a  passing  electric  wave  just  as  iron  wires  held 
in  the  magnetic  meridian  become  magnetized ;  pointed  in  the  direction  of 
the  station  the  magnetic  effect  would  be  zero.  It  has  been  proposed  to 
utilize  this  fact,  both  as  a  detector  of  electric  waves  and  of  their  direction, 

Any  conducting  wire  held  perpendicular  to  the  earth  will  be  cut  at 
right  angles  by  the  magnetic  lines  of  force  and  will  have  electric  charges 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  67 

induced  in  it  which  will  create  currents,  and  it  is  by  means  of  the  cur- 
rents induced  in  vertical  conductors  that  electric  waves  are  usually 
detected. 

A  vertical  wire  thus  situated  also  has  a  difference  of  potential  created 
in  its  ends  since  it  joins  two  points  of  the  advancing  wave  whose  electric 
potentials  differ. 

This  is  also  the  case  in  a  horizontal  wire,  if  in  the  line  joining  its  posi- 
tion with  the  source  of  radiation,  A  very  long  horizontal  wire  so  placed 
might  have  stationary  waves  like  those  of  fig.  18c  set  up  in  it. 

The  total  electric  is  equal  to  the  total  magnetic  energy  in  an  advancing 
vrave. 

If  two  horizontal  conducting  plates  forming  a  condenser  are  in  the 
path  of  the  wave,  they  will  have  electro-static  charges  of  different  poten- 
tials induced  in  them.  This  potential  difference  will  vary  with  their 
vertical  distance  apart.  If  these  plates  are  joined  by  a  conductor,  electric 
currents  will  be  produced  in  it. 

We  see,  therefore,  that  there  should  be  at  least  three  ways  of  detecting 
electric  waves:  (a)  By  placing  conductors  at  right  angles  to  the  mag- 
netic field;  (b)  By  placing  conductors  parallel  to  the  electric  field;  (c) 
By  adding  to  conductors  at  right  angles  to  the  magnetic  field,  conducting 
planes  forming  condensers  at  right  angles  to  the  electric  field. 

It  would  seem  that  by  the  last  method  we  should  be  able  to  abstract  the 
greatest  amount  of  energy  from  an  electric  wave  and,  therefore,  be  able 
to  detect  it  at  the  greatest  distance  from  its  source.  Methods  (a)  and  (b) 
coincide  since  vertical  conductors  are  at  the  same  time  at  right  angles  to 
the  magnetic  field  and  parallel  to  the  electric  field. 

From  the  good  receiving  results  obtained  by  the  use  of  long  horizontal 
conductors,  with  a  comparatively  limited  vertical  portion,  it  seems  that  the 
parts  of  the  earthed  waves  near  the  earth  (see  fig.  33)  travel  at  a  slower 
rate  than  the  higher  parts  and  the  waves  are  bent  over  as  if  fig.  33  were 
reversed,  cutting  the  horizontal  wires  at  something  less  than  a  right 
angle.    However,  this  subject  awaits  more  complete  investigation. 

108.  It  will  be  readily  seen  that  the  induction  of  currents  in  another 
aerial,  however  great  the  distance  from  the  inducing  aerial,  is  not  greatly 
different  from  the  inductive  actions  of  the  wires  A  B  and  C  D  on  each 
other,  which  were  discussed  in  the  preceding  chapter. 

It  was  there  pointed  out  that  inductive  actions  caused  by  ether  move- 
ments could  have  no  limits,  however  small  they  might  be  at  great  dis- 
tances. In  other  words,  every  change  of  current  sends  out  some  non- 
returnable  energy.  Oscillating  circuits  of  high  frequency  send  out  more 
non-returnable  energy  and  radiate  better  than  those  of  low  frequency. 
Open  oscillating  circuits  radiate  faster  than  closed  oscillating  circuits. 


68  MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

RECEIVING  CIRCUITS. 

109.  In  practically  all  cases,  except  at  a  few  large  stations,  the  same 
aerial  wire  is  used  for  both  sending  and  receiving. 

The  advancing  waves  of  electric  and  magnetic  force  from  the  sending 
aerial  cut  the  receiving  aerial  and  induce  in  it  oscillating  currents.  If 
the  receiving  circuit  has  the  same  period  as  that  of  the  passing  waves,  the 
induced  oscillating  currents  in  the  aerial  will  increase  until  the  energy 
dissipated  per  oscillation,  by  re-radiation,  resistance,  and  transfer  to  other 
parts  of  the  receiving  circuit,  is  equal  to  that  received  per  wave. 

If  the  receiving  aerial  circuit  is  directly  or  inductively  connected  to  a 
closed  oscillating  circuit  to  which  part  of  the  energy  received  per  wave  is 
transferred  during  each  oscillation  instead  of  being  re-radiated,  this 
closed  oscillating  circuit  will  absorb  energy,  and  if  its  period  is  equal  to 
that  of  the  arriving  waves  the  oscillations  will  increase  in  amplitude  with 
each  half  period,  since  a  closed  circuit  radiates  slowly.  If  a  detector  is 
placed  in  either  the  open  or  closed  circuit  so  that  the  oscillating  currents 
produce  differences  of  potential  at  its  terminals  and  the  maximum  ampli- 
tude of  the  oscillation  set  up  is  sufficient  to  make  it  function,  the  passing 
of  groups  of  wave  trains  separated  into  dots  and  dashes  at  the  sending 
station  can  be  detected  at  the  receiving  station. 

At  the  sending  station  the  closed  circuit  furnishes  energy  to  the 
radiating  circuit,  which  sends  it  out  in  the  shape  of  electric  waves. 

At  the  receiving  station  this  radiating  circuit  absorbs  energy  from 
the  passing  waves  and  transfers  to  the  closed  circuit  part  of  what  it 
absorbs. 

It  is  evident  that  no  spark  gap  is  required  in  the  closed  receiving  cir- 
cuit and  that,  since  no  high  potentials  nor  heavy  currents  need  be 
provided  for,  it  is  not  necessary  that  the  receiving  inductances  and 
condensers  should  have  the  same  dimensions  or  arrangement  as  those  in 
the  sending  circuits.  But  in  all  other  features  receiving  circuits  are  the 
exact  analogue  of  sending  circuits  and  the  detector  could  occupy  the  place 
of  the  spark  gap. 


Chapter  III. 

ELECTEIC  UNITS  AND  THEIR  RELATION  TO  EACH  OTHER. 

110.  Fleming  says  "  exact  measurement  is  the  very  life  and  soul  of  all 
technical  applications  of  science.'' 

Our  attention  has  thus  far  been  concentrated  on  the  quality  rather 
tlan  the  quantity  of  the  electro-magnetic  actions  under  discussion.  Be- 
fore proceeding  further  it  is  necessary  to  consider  the  standards  of 
measurement  adopted  and  their  relation  to  each  other. 

111.  Electric  and  magnetic  actions  being  forms  of  energy,  and  being 
mutually  convertible,  as  we  have  seen,  are  subject  to  all  the  laws  govern- 
ing transformations  of  energy. 

Wurlc  is  done  when  conductors  are  moved  in  magnetic  fields,  the  re- 
sistance to  movement  and  the  amount  of  movement  determining  the 
amount  of  work  done. 

The  unit  of  mechanical  work  is  a  foot-pound,  by  which  name  we 
designate  the  work  done  in  lifting  1  pound  1  foot  against  the  action  or 
force  of  gravity. 

Force,  by  which  we  mean  the  cause  6i  action  or  movement  (pulling  or 
pushing  ability),  is  measured  in  pounds,  and  force  multiplied  by  the 
distance  through  which  it  acts  is  wor]c.  Lifting  10  pounds  10  feet=100 
foot-pounds.  Exerting  a  push  of  10  pounds  for  100  feet  =  1000  foot- 
pounds. 

The  amount  of  work  done  in  a  given  time — that  is,  the  rate  of  doing 
work — is  called  power.  The  unit  of  mechanical  power  we  call  a  horse- 
power, and  it  represents  a  rate  of  doing  work  equal  to  33,000  foot-pounds 
per  minute,  or  550  foot-pounds  per  second. 

In  the  above  definitions  of  work  and  power  the  units  of  distance, 
weight  (or  mass),  and  time  are  the  foot,  pound,  and  minute,  all  of  which 
are  defined  by  law  and  are  called  fundamental  units. 

112.  Another  system  of  units,  proposed  by  the  British  Association  for 
the  Advancement  of  Science  and  now  generally  used  in  electrical 
measurements,  is  based  on  the  centimeter,  gram,  and  second,  and  is 
usually  called  the  c.  g.  s.  system.  The  use  of  this  system  is  authorized 
bv  law  and  is  universal  in  scientific  work. 


70  MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

The  following  relations  exist  between  the  two  sets  of  units : 
1  foot      =   30.48  centimeters,  approximately. 
1  pound  =453,59  grams,  approximately. 
1  minute  =   60        seconds.* 

The  units  of  length  and  weight  in  the  United  States  are  kept  at  the 
Bureau  of  Standards  in  "Washington,  and  the  unit  of  time  is  determined 
by  the  Naval  Observatory  in  the  same  city. 

The  unit  of  force  in  the  c.  g.  s.  system  is  that  force  which,  acting  on  a 
gram  mass  for  1  second  gives  it  a  velocity  of  1  centimeter  per  second. 
This  force  is  called  a  dyne. 

The  force  of  gravity  acting  on  a  gram  mass  for  1  second  will  give  it 
a  velocity  of  32.2  feet  per  second  =  approximately  981  centimeters  per 
second;  therefore  the  force  of  gravity  is  equal  to  981  dynes  and  the  pull 
of  a  dyne  represented  as  a  weight  is  equal  to  -^\^  of  a  gram. 

The  pull  of  a  pound,  which  equals  453.59  grams,  must  be  equal  to  that 
of  453.59x981  =  approximately  445,000  dynes. 

The  unit  of  worTc  in  the  c.  g.  s.  system  is  the  work  done  in  overcoming 
the  force  of  1  dyne  through  1  centimeter,  and  is  called  an  erg.  In  other 
words,  an  erg  is  the  work  done  in  lifting  ^\^  of  a  gram  1  centimeter. 

An  erg  by  definition  is  a  dyne  overcome  through  a  centimeter,  and  we 
see  that  a  foot-pound  is  445,000  dynes  overcome  through  30.48  centi- 
meters; therefore  a  foot-pound  equals  445,000x30.48  =  approximately 
13,570,000  ergs,  and  a  horse-power,  which  equals  550  foot-pounds, 
per  second=13,570,000x  550  =  approximately  7,460,000,000  ergs  per 
second. 

113.  The  c.  g.  s.  units  of  length  (centimeter),  time  (second),  force 
(dyne),  and  work  (erg)  are  employed  to  define  the  absolute  units  used 
in  electrical  measurements.  These  are  electro-motive  force,  current, 
and  resistance.  (Art.  3,  art.  29.)  From  these  are  derived  the  so-called 
practical  units  in  daily  use — volt,  ampere,  and  olim. 

On  account  of  the  fact  that  the  names  adopted  for  the  practical  electro- 
magnetic units  are  all  names  of  noted  scientists  and  not  related  to  nor 
in  any  way  descriptive  of  the  qualities  they  are  used  to  designate,  their 
acquirement  must  be  entirely  a  feat  of  memory.  They  can  be  more  easily 
remembered  by  associating  them  with  the  names  of  the  theoretical  or 
absolute  units.  As,  for  instance,  we  say  an  E.  M.  F.  of  125  volts,  a  current 
of  40  amperes,  a  resistance  of  10  ohms. 

*  The  unit  of  time  is  based  on  a  fundamental  unit,  being  a  fraction  of  tlie 
cime  of  a  revolution  of  the  earth,  and  this  unit  is  common  to  both  systems. 
The  foot  and  the  pound  are  really  arbitrary  units.  The  centimeter  is  a 
fraction  of  a  fundamental  unit,  namely,  of  the  distance  from  the  equator  to 
che  north  pole  on  a  certain  meridian.  The  gram  is  the  weight  of  a  cubic 
centimeter  of  distilled  water.    It  is  an  arbitrary  unit. 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  71 

By  agreement  among  electricians,  electro-motive  force  is  represented 
by  the  letter  E;  electric  current  by  the  letter  I;  resistance  to  the  flow  of 
electricity  by  the  letter  R;  time  by  the  letter  T ;  work  by  the  letter  W ; 
power  by  the  letter  P.  The  object  now  is  to  determine  the  relation  of  these 
quantities  to  each  other, 

114.  We  know  that  it  requires  work  to  move  conductors  in  magnetic 
fields,  or  one  magnet  in  the  vicinity  of  another,  and  the  movement 
generates  an  E.  M.  F.  in  the  conductor,  and  also  a  current,  if  the  conductor 
forms  a  closed  circuit.  And  we  also  know  that  the  amount  of  current 
produced  by  a  given  E,  M.  F.  depends  on  the  resistance  of  the  conductor 
(art.  29). 

We  say  that  the  E,  M.  F.  and  current  are  produced  in  the  circuit  because 
it  cuts  the  lines  of  force  of  the  magnetic  field. 

We  must,  therefore,  have  a  definite  idea  or  agreement  as  to  exactly 
what  is  meant  by  the  term,  lines  of  magnetic  force,  and  how  they  are  con- 
nected with  E.  M.  F.  and  current. 

The  physical  basis  for  the  term  is  the  action  of  iron  filings  in  the  field 
of  a  magnet  (art.  7,  fig.  6),  but  to  make  a  definite  basis  for  measurement  it 
has  been  agreed,  first,  that  a  unit  magnet  pole  shall  be  one  that  when  placed 
at  a  distance  of  1  centimeter  in  air  from  a  like  pole  of  equal  strength,  is 
repelled  by  a  force  of  1  dyne. 

Second,  if  a  unit  pole,  as  defined  above,  is  placed  in  a  field  of  force  of 
such  strength  that  it  is  acted  upon  (attracted  or  repelled)  by  a  force  of 
1  dyne,  such  a  field  is  a  unit  field  and  shall  be  held  to  contain  one  line  of 
force  per  square  centimeter. 

It  is  further  agreed,  third,  that  unit  E.  M.  F.  shall  be  that  generated 
by  moving  a  conductor  across  unit  field,  so  that  it  cuts  1  square  centimeter 
(1  line  of  force)  per  second. 

Fourth,  if  this  conductor  forms  part  of  a  closed  circuit,  and  if  the  cur- 
rent generated  by  this  unit  E.  M.  F.  is  such  as  to  cause  the  movement  of 
the  conductor  to  be  resisted  by  a  force  of  1  dyne,  it  is  agreed  that  the  con- 
ductor has  unit  resistance  and  that  the  current  produced  is  unit  current. 

The  work  done  is  1  erg  per  second,  equal  to  a  dyne  (-g^  gram),  lifted 
1  centimeter. 

Since  power  is  rate  of  doing  work,  we  can  say  it  requires  unit  power  to 
produce  unit  E.  M.  F.  or  unit  current  in  a  circuit  of  unit  resistance. 

115.  Let  fig.  15  represent  unit  magnetic  field  between  two  magnet  poles 
N  and  S.  Let  C  D  represent  a  conductor  one  centimeter  in  length  mov- 
ing at  right  angles  to  this  field  at  the  rate  of  one  centimeter  per  second, 
and  making  sliding  connections  at  its  ends  with  a  very  heavy  conductor 
whose  resistance,  as  compared  with  C  D,  is  so  small  that  it  can  be  neg- 
lected and  the  resistance  of  the  circuit  considered  as  concentrated  in  C  D. 

Then,  if  it  requires  a  pull  of  1  dyne  (1/981  gram)  to  keep  C  D  moving 


72 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


at  the  rate  of  one  centimeter  per  second,  C  D  has  unit  resistance,  unit 
current  flows,  and,  by  definition,  unit  E.  M.  F.  is  generated. 

116.  If  the  speed  of  C  D  is  doubled,  the  E.  M.  F.  is  doubled  and  the  cur- . 
rent  (as  shown  by  the  effects)  is  also  doubled,  we  can  express  this  by  say- 
ing :   (a)  Current  varies  directly  as  E.  M.  F. 


i   i    l^i       1/ 


Fig.  15. 


If  the  size  of  C  D  is  doubled  (the  speed  and,  therefore,  E.  M.  F.  remain- 
ing the  same)  the  resistance  is  reduced  to  one-half,  and  we  find  that  the 
current  is  doubled  as  before;  we  say:    (b)   Current  varies  inversely  as 

F    M   F 
resistance.    Combining  (a)  and  (b)  we  can  say  current^  — "^-r^ — ~  or  I 
°  ^   '  ^   ^  •'  resistance 

=  -(1). 

Equation  (1)  is  the  fundamental  electrical  equation  and  states  in 
mathematical  form  what  is  known  as  Ohm's  law,  viz. :  "  The  current  in 
any  circuit  varies  directly  as  the  electro-motive  force,  and  inversely  as 
the  resistance  in  the  circuit.'^ 

117.  We  also  find  that  doubling  the  current  doubles  the  opposition  to 
movement  and,  other  things  remaining  the  same,  doubles  the  work  pei 
second,  or  the  power.    Power,  therefore,  varies  directly  as  the  current. 

Doubling  the  speed  of  movement  doubles  the  electro-motive  force  and 
also  the  current,  but  it  quadruples  the  power  or  work  done  per  second  since 
it  represents  a  pull  of  2  dynes  through  2  centimeters  in  1  second.  Power 
therefore,  varies  directly  as  the  E.  M.  F.,  as  well  as  directly  with  the  cur- 
rent, and  we  say  that  it  varies  as  their  product,  or  P  =  I  E  (2)  or  from  (1) 


R 


andP^C'R. 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  73 

The  foregoing  are  physical  facts  determined  by  observation  and  experi- 
ment. 

118.  Since  magnetic  fields  containing  20,000  lines  of  force  per  square 
centimeter  can  be  obtained,  a  rate  of  cutting  of  one  line  per  second 
gives  too  small  a  unit  of  E.  M.  F.  for  practical  use. 

On  the  other  hand,  the  current  necessary  to  produce  a  resistance  of 
1  dyne  to  this  slow  movement  in  unit  field  is  somewhat  large,  therefore 
to  replace  the  theoretical  or  absolute  units,  as  defined  in  art.  114,  the 
so-called  practical  units  have  been  adopted. 

VOLT. 

The  practical  unit  of  E.  M.  F.  is  the  volt  and  is  the  E.  M.  F.  generated 
when  lines  of  force  are  cut  at  the  rate  of  100,000,000  per  second. 

AMPERE. 

The  practical  unit  of  current  is  the  ampere  and  is  one-tenth  of  the 
theoretical  or  absolute  unit. 

OHM. 

E 

In  order  to  maintain  the  truth  of  the  equation  /= -^  (1),  the  prac- 

tical  unit  of  resistance,  which  is  the  ohm,  is  taken  as  1,000,000,000 
times  the  theoretical  or  absolute  unit. 

Ohm's    law    then    still    remains    true.      7=    „    or    amperes  =  -; 

R  ^  ohms, 

because  this  equation  in  terms  of  the  absolute  units  is  —  (amperes)  = 

E  X  100,000,000  (volts)        ^  •  ,    .    ,,  r      E       „,,        .        . 

-n^-,  r^.^r  nnr! nnn  /  1, \  >  which  IS  thc  samc  as  i  =  -„" .     1  lie  size  of 

B  X  1,000,000,000  (ohms)  '  R 

the  units  has  been  changed,  but  the  proportion  between  them  is  the  same 

as  before. 

WATT. 

The  practical  unit  of  power  is  the  watt,  which  is  the  ergs  of  work 

done  per  second  when  1  ampere  is  made  to  flow  with  an  E.  M.  F.  of  1  volt. 

This  in  ergs  (see  equation  (2))  equals  unit  E.  M.  F.x  100,000,000  X 

^ ,  or  10,000,000  ergs  per  second.     Therefore  1  watt  equals 

10,000,000  ergs  per  second.  The  power  expended  in  any  circuit  in  watts 
equals  the  product  of  the  volts  and  amperes  in  the  circuit,  or  P=IE  (2). 

Ten  million  ergs  of  work  is  called  a  joule.  Therefore  a  watt=l  joule 
per  second. 

We  have  seen  that  1  H.  P.  =  7,460,000,000  ergs  per  second.  There- 
fore 1  H.  P.=  746  watts.  1  watt  =  approximately  0.737  foot-pounds  per 
second. 


74  MANUAL    OF    RADIO    TELEGRAPHY   AND   TELEPHONY, 

119.  After  having  selected  the  practical  units,  it  became  necessary,  for 
the  purpose  of  comparison  and  for  everyday  use,  to  represent  them  in 
practical  form,  because  the  accurate  measurement  of  dynes  and  ergs  is  a 
very  difficult  matter  practically,  but  it  can  be  done  in  accordance  with 
definitions  given  in  art.  112. 

Art.  114  indicates  how  to  measure  the  strength  of  magnetic  fields  and 
how  to  determine  and  compare  E.  11.  Fs.  and  currents  by  the  ergs  of  work 
done  in  creating  them.  A  volt  or  an  ampere  can  thus  be  definitely  created. 
The  reproduction  of  standards  of  measurement  is  assisted  by  the  following 
facts:  (a)  The  resistance  of  a  conductor  kept  at  a  constant  temperature 
is  found  to  depend  only  on  its  length  and  area  of  cross  section,  so  that 
standards  of  resistance  are  easily  reproduced. 

(b)  The  current  from  certain  primary  batteries  is  found  to  be  constant 
when  their  terminals  are  connected  by  the  same  wire : 

Since  current  and  resistance  are  constant,  the  voltage  of  such  cells 
must  be  constant,  and  this  voltage  once  determined  by  comparison  with 
absolute  volts  as  determined  above,  we  have  at  once  a  practical  concrete 
standard  of  E.  M.  F. 

(c)  It  is  found  that  the  decomposition  of  an  electrolyte  (art.  1),  by  an 
electric  current,  always  results  in  the  separation  or  deposit  of  exactly 
equal  quantities  of  the  constituents  of  the  electrolyte  for  equal  quantities 
of  current.  The  deposit  in  a  certain  time,  being  weighed,  serves  as  a 
very  accurate  measurement  of  the  amount  of  electricity  which  passes  in 
that  time,  and  consequently  affords  a  very  accurate  means  of  comparing 
electric  currents.  When  1  ampere  determined  as  above  is  passed  through 
a  given  electrolyte,  the  weight  of  material  deposited  gives  us  at  once  a 
practical  standard  of  current. 

E 

120.  On  account  of  the  relation  1=  ^  (1)  between  amperes,  volts,  and 

ohms  in  a  circuit,  if  any  two  of  them  are  known  the  other  is  also  known, 
so  that  only  two  measurements  of  concrete  units  are  required.  The 
question  of  which  two  should  be  selected  and  the  exact  form  that  each 
should  take  has  been  the  subject  for  discussion  at  a  number  of  inter- 
national conferences,  the  latest  of  which  has  recommended  that  only 
two  electrical  units  shall  be  chosen  as  fundamental  units,  viz.,  the  inter- 
national ohm  defined  by  the  resistance  of  a  column  of  mercury,  and  the 
international  ampere  defined  by  the  deposition  of  silver. 

The  volt  to  be  defined  as  the  E.  M.  F.  which  produces  an  electric  cur- 
rent of  1  ampere  in  a  conductor  whose  resistance  is  1  ohm. 

Different  methods  of  measurements  produce  slight  differences  in  the 
values  of  the  standards,  but  the  values  recognized  by  law  in  the  United 
States  are  as  follows : 


MANUAL    OF    RADIO    TELEGRAPHY   AND   TELEPHONY.  75 

The  standard  (international)  ohm  is  the  resistance  offered  to  an  un- 
varying electric  current  by  a  column  of  mercury  at  the  temperature  of 
melting  ice — 14.4521  grams  in  mass — of  a  constant  cross-sectional  area, 
and  of  a  length  of  106.3  centimeters. 

The  standard  (international)  ampere  is  the  unvarying  current  which, 
when  passed  through  a  solution  of  nitrate  of  silver  in  water  in  accordance 
with  certain  specifications,  deposits  silver  at  the  rate  of  0.001118  of  a 
gram  per  second. 

As  previously  stated,  a  volt  is  the  E.  ]\I.  F.  which  if  steadily  applied 
to  a  conductor  whose  resistance  is  1  ohm  will  produce  a  current  of  1 
ampere;  but  a  concrete  standard  for  the  volt  is  also  recognized  by  law, 
it  being  specified : 

That  the  electrical  pressure  at  a  temperature  of  15°  centigrade  between 
the  poles  or  electrodes  of  the  voltaic  cell  known  as  Glade's  cell,  prepared 
in  accordance  with  certain  specifications,  may  be  taken  as  not  differing 
from  a  pressure  of  1.434  volts  by  more  than  1  part  in  1000. 

The  latest  international  conference  has  recommended  the  adoption 
of  the  Weston  cadmium  cell  as  preferable  to  the  Clark  for  a  standard 
cell.    The  Weston  cell  has  an  E.  M.  F.  of  1.018  volts  at  20°  C. 

Standard  resistance  wires  having  a  known  ratio  to  the  legal  ohm  are 
made,  and  these,  with  standard  cells,  are  used  for  calibrating  volt  meters 
and  ammeters,  which  are  the  names  given  to  the  galvanometers  for  indi- 
cating automatically  the  E.  M.  F.  and  cuiTent  in  any  circuit.  In  this 
way  electrical  values  are  made  uniform  throughout  the  country. 

121.  In  addition  to  the  volt,  the  ampere,  the  ohm,  the  watt,  and  the 
joule  other  practical  units  have  been  adopted,  the  most  important  of 
which,  for  our  purposes,  are : 

COULOMB. 

The  unit  of  quantity,  the  coulomb,  which  is  the  amount  of  electricity 
passing  any  point  in  a  second  when  1  ampere  is  flowing  in  the  circuit. 

FARAD. 

The  unit  of  capacity,  the  farad.  A  condenser  is  said  to  have  a  capacity 
of  1  farad  when  1  coulomb  of  electricity  will  charge  it  to  a  potential 
of  1  volt. 

(Potential  and  E.  M.  F.  are  in  some  senses  identical,  one  being  the 
passive  and  the  other  the  active  state.  An  E.  M.  P.  is  the  result  of 
difference  of  potential.) 

If  this  definition  were  in  terms  of  the  absolute  units,  that  for  capacity 
would  read : 

A  condenser  is  said  to  have  unit  capacity  when  one  unit  of  electricity 
will  charge  it  to  unit  potential. 


76  MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

Since  by  definition  a  condenser  has  a  capacity  of  one  farad  when  one- 
tenth  of  the  absolute  unit  of  electricity  charges  it  to  a  potential  of 

100,000,000,  a  farad  must  equal  — ,  x  roo~00(U)f)n  ~^^'^  absolute  units 
of  capacity.* 

HENRY. 

122.  The  unit  of  self-induction,  the  henry.  A  circuit  is  said  to  have  a 
self-induction  of  1  henry  when,  if  the  current  in  it  is  varied  at  the  rate 
of  1  ampere  per  second,  the  induced  E.  M.  F. — that  is,  the  counter  or 
reacting  E.  M.  F. — tending  to  oppose  the  change  is  1  volt. 

The  definition  of  self-induction  in  terms  of  the  absolute  units  would  be : 

A  circuit  is  said  to  have  unit  self-induction  when,  if  the  current  in 
it  is  varied  at  the  rate  of  one  unit  per  second,  the  E.  M.  F.  of  self-induc- 
tion is  unity. 

Since  by  definition  a  circuit  has  a  self-induction  of  one  henry,  when,  if 
the  current  is  varied  at  the  rate  of  one-tenth  of  unit  current  per  second, 
the  absolute  E.  M.  F.  of  self-induction  is  100,000,000  such  a  circuit  would 
have  an  absolute  E.  M.  F.  of  self-induction  10  times  as  great,  or 
1,000,000,000,  if  the  current  instead  of  being  varied  at  the  rate  of  one- 
tenth  unit  per  second  were  varied  at  the  rate  of  one  unit  per  second. 
Therefore  the  unit  of  self-induction,  the  henry,  is  equal  to  1,000,000,000 
=  10®  absolute  units  of  self-induction. 

By  agreement  among  electricians  self-induction  is  represented  by  the 
letter  L;  capacity,  by  the  letter  C. 

Self-induction,  when  expressed  in  terms  of  the  fundamental  units  of 
length,  mass,  and  time,  has  the  dimensions  of  a  length,  and  the  prac- 
tical unit  of  self-induction  was  formerly  called  a  quadrant  on  account 
of  the  fact  that  in  the  metric  system,  an  earth  quadrant — i.  e.,  the  dis- 
tance from  the  equator  to  the  north  pole  =  1,000,000,000  centimeters, 
and  since  the  henry  =  1,000,000,000  absolute  units  of  self-inductance,  it 
was  said  to  =1,000,000,000  centimeters. 

In  this  notation  a  millihenry  =  1,000,000  centimeters.     (See  art.  125.) 

123.  The  units  which  have  been  considered  in  this  chapter  have  been 
derived  from  the  relations  between  electric  currents  and  magnetic  fields 
and  are  called  electro-magnetic  units.  Another  S3'stem  of  units,  also 
based  on  the  centimeter,  gram,  and  second,  called  electrostatic  units, 
is  in  use.  The  relation  between  the  absolute  units  of  quantity  in  the  two 
systems  is  the  velocity  of  light  in  centimeters  per  second.  This  velocity 
is  30,000,000,000,  or  3x10^°  centimeters  per  second,  and  the  electro- 
magnetic unit  of  quantity  =  3  xlO^"  electro-static  units. 

*  When  quantities  are  dealt  with  having  a  large  number  of  ciphers  either 
before  or  following  the  significant  figures  it  is  convenient  to  express  them  as 
multiplied  by  some  power  of  ten,  i  e..  10  =  lOS  100  =  10',  ^ig=lO-\^ij=  10-*. 
etc. 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  77 

The  coulomb,  being  one-tenth  of  the  absolute  unit,  =3x10®  electro- 
static units. 

The  electro-magnetic  unit  of  potential  is  -g^  of  the  electro-static  unit. 

In  both  systems  a  condenser  is  said  to  have  unit  capacity  when  unit 
quantity  of  electricity  charges  it  to  unit  potential. 

From  the  definition  of  a  farad,  given  in  art.  121,  we  see  that  the 
quantity  of  electricity  in  a  condenser  equals  in  coulombs  the  potential 

Q 
in  volts  multiplied  by  the  capacity  in  farads,  or  Q  =  EC,  .'.C=  -p  .    Sub- 
stituting for  Q  and  E  their  unit  values  in  electro-static  units  given 

3X10* 
above,  C  = ^ =  9x10",  or  the  practical  electro-magnetic  unit  of 

capacity  is  9  x  10"  times  as  large  as  the  electro-static  unit. 

The  capacity  of  spherical  bodies  is  found  to  vary  as  their  radii,  and 
in  the  electro-static  system  a  sphere  of  1  centimeter  radius  has  unit 
capacity;  therefore  the  capacity  of  a  sphere  may  be  expressed  by  its 
radius  in  centimeters,  and  capacities  are  still  expressed  by  some  writers 
and  manufacturers  by  the  radius  in  centimeters  of  the  equivalent  sphere. 

A  condenser  having  a  capacity  of  1  farad  has  a  capacity  equal  to  that 
of  a  sphere  having  a  radius  of  9x10"  centimeters. 

A  microfarad  (see  art.  125)  =10"'^  farads,  is  equal  to  a  capacity  9x 
10"XlO-"  =  9xlO%  or  900,000  centimeters  in  electro-static  units. 

The  earth's  radius  is  approximately  65x10'  centimeters;  its  capacity 
should  be  approximately  700  microfarads. 

124.  This  difference  in  nomenclature  is  very  confusing,  but  it  exists 
particularly  with  reference  to  the  two  qualities  of  self-induction  and  capac- 
ity with  which  wireless  telegraphy  is  intimately  concerned.  Microfarads 
and  millihenrys  will  be  used  in  this  book,  and  where  centimeters  are  found 
as  in  some  catalogues  and  some  books  on  electricity,  the  relations  here 
given — 1  millihenry  =  1,000,000  centimeters  electro-magnetic  units;  1 
microfarad  =  900,000  centimeters  electro-static  units — will  enable  one  set 
of  units  to  be  converted  into  the  other. 

The  entire  system  of  units  used  in  electrical  measurements  is  a  monu- 
ment to  the  ingenuity  of  scientists,  but  productive  of  many  difficulties 
to  students.    Careful  study  is,  therefore,  necessary. 

125.  While  the  volt,  the  ampere,  and  the  ohm  are  really  practical  units, 
the  farad  and  henry  are  too  large  for  practical  use. 

It  would  take  a  very  large  condenser  to  have  a  capacity  of  1  farad 
and  a  coil  of  many  turns  to  have  a  self-induction  of  1  henry.  Sub- 
divisions of  the  farad  and  henry  are  in  practical  use. 

Multiples  and  subdivisions  of  the  other  units  are  also  frequently  used, 
and  for  this  purpose  the  prefLxes  kilo,  meaning  1000;  mega,  meaning 


78  MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

1,000,000 ;   milli,   meaning  j^  ,   and  micro,   meaning  ^  ^^^  ^^^  ,  are 
added  to  the  units,  and  such  terms  as — 


kilowatt 
kilo  volt 
megohm 

=  1,000  watts, 

=  1,000  volts. 

=  1,000,000  ohms. 

millivolt 

=  i,Joo  ^°^*' 
1 

milliampere=  .  ^^  ampere, 
millihenry    =  ^^qq  ^^enry, 

microfarad  =  i^oO^OO  ^"''^' 
microsecond=^-^^^-^^^  second, 

are  in  common  use.  The  most  common  practical  units  of  capacity  and 
self-induction  (the  qualities  of  electric  circuits  with  which  wireless 
telegraphy  is  principally  concerned,  because  they  determine  the  period 
of  vibration)  are  the  microfarad  and  the  millihenry,  but  even  these  are 
too  large  for  convenience. 

The  terms  mil,  meaning  inch;  micron,  meaning  ^-^         —  meter; 

circular  mil,  meaning  area  of  cross  section  of  a  wire  having  a  diameter  of 

■.^„„    inch,  are  also  in  general  use  among  electricians. 

126.  The  E.  M.  F.  (volts)  in  any  circuit  connected  with  a  dynamo 
depends  only  on  the  rate  of  cutting  of  lines  of  force  (strength  of  field 
and  rate  of  revolution). 

The  resistance  (ohms)  in  any  circuit  depends  only  on  the  material, 
cross  section,  and  length  of  the  conductor  forming  the  circuit. 

The  current  (amperes)  in  any  circuit  depends  only  on  the  E.  M.  F. 
and  the  resistance  in  the  circuit. 

The  power  (watts)  in  any  circuit  depends  only  on  the  E.  M.  F.  and 
current  in  the  circuit. 

The  self-induction  (henries)  in  any  circuit  depends  only  on  the  shape 
and  length  of  the  circuit,  on  the  magnetic  permeability  (art.  25)  of  the 
material  surrounding  and  inclosed  by  the  circuit,  on  the  amount  of 
this  material  and  on  the  position  of  the  circuit  relative  to  other  circuits. 

The  capacity  (farads)  in  any  circuit  depends  only  on  the  shape  and 
area  of  its  surface,  on  the  electric  permeability  (art,  46)  of  the  material 
surrounding  the  circuit,  on  the  amount  and  location  of  this  material  (the 
dielectric),  and  on  the  position  of  the  circuit  relative  to  other  conductors. 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY.  79 

(Straight  wires  are  said  to  have  distributed  inductance  and  capacity, 
coiled  wires  have  concentrated  inductance,  and  condensers  have  con- 
centrated capacity.) 

The  coulombs  in  a  charged  condenser  or  circuit  depend  only  on  the 
capacity  and  potential  of  the  condenser  or  circuit. 

127.  From  the  foregoing  we  can  make  up  a  table  of  values  as  follows  :— 

A  volt=  100,000,000  =  10«  absolute  units  of  E.  M.  P. 

An  ohm  =1,000,000,000  =  10"*  absolute  units  of  resistance. 

An  ampere  =  y\  =10"^  absolute  units  of  current. 

A  watt=a  volt  X  an  amp.  =  10^X10-^  =  10^  absolute  units  of  work 
per  8econd=l  Joule  per  second=  y^  H.  P.  =  0.737  foot-pounds  pei 
second, 

A  horse  power=746  watts. 

A  kilowatt=1000  watts. 

^  ^^'^^=  1,000,000,000  =^^"  '^^^^^^  "°^*^  '^  ^^P^^^*y- 

A  farad  in  electro-static  units  =  9xl0"  centimeters. 

A  microfarad  =    aaa  nAr>  farad=10-^''  absolute  units  of  capacity. 

A  microlarad  in  electro-static  units  =  900,000  centimeters. 
A  henry  =1,000,000,000=10"  absolute  units  of  self-induction. 

A  millihenry  =  :.^.   henry  =  10'  absolute  units  of  self-induction. 

A  millihenry  in  electro-magnetic  units  =  1,000,000  centimeters. 

A  standard  Leyden  jar  or  plate  having  a  capacity  of  .002  microfarad 
has  been  adopted  for  naval  use.  In  electro-static  notation  1  standard  jar 
has  a  capacity  of  1800  centimeters. 


Chapter  IV. 

CAPACITY  AND  SELF-INDUCTION. 

FUNDAMENTAL  EQUATION   OF  WIRELESS  TELEGRAPHY. 

128.  It  was  stated  in  art.  56  that  the  period  of  electrical  vibration  of 
any  circuit  depends  onl}'  on  the  capacity  and  self-induction  of  the  circuit. 

Lord  Kelvin  proved  many  years  ago  that  when  the  ratio  of  the 
resistance  to  the  self-induction  of  a  circuit  is  small,  the  circuit  will 
vibrate  in  a  certain  period,  which  is  found  to  be  equal  in  seconds  to 
'lirV LC  (3)  when  L  is  measured  in  henries,  C  is  measured  in  farads, 
7r  =  3.1416.  This  is  called  the  fundamental  equation  of  wireless  teleg- 
raphy.    (See  table  7,  appendix  A.) 

If  R  is  greater  than  ^  J  ^  the  circuit  will  not  vibrate  at  all.     For 

instance,  when  a  condenser  is  discliarged  through  a  wire  of  great  resist- 
ance the  charge  leaks  out  slowly  witliout  any  oscillation. 

A  nonoscillatory  condenser  discbarge,  as  compared  with  an  oscillatory 
discharge,  is  like  the  flow  of  molasses  into  a  jar  as  compared  with  a  large 
and  sudden  flow  of  water  into  a  similar  jar.  One  takes  up  a  position  of 
equilibrium  slowly  but  surely,  while  the  otber  vibrates  and  splashes  and 
only  settles  down  after  a  considerable  period. 

Equation  (3)  shows  that  a  circuit  having  a  self-induction  of  1  henry 
and  a  capacity  of  1  farad  would  have  a  period  of  27r=  6.2832  seconds. 
Its  wave  length  would  be  1,168,000  miles. 

The  standard  wave  length  originally  adopted  for  naval  wireless  tele- 
graph circuits  was  320  meters;  the  period  was  approximately  -g-iyi/oiFTF 
second,  that  is,  they  made  approximately  900,000  complete  vibrations 
per  second.  The  usual  capacity  in  these  circuits  was  0.014  microfarad 
(seven  0.002  microfarad  jars  in  parallel).  Therefore  the  self-induction 
must  have  been  0.0022  millihenry.  The  standard  wave  length  was  in- 
creased first  to  425,  then  to  600  and  recently  to  750  meters  for  large  ships. 

It  will  be  noted  that  the  period  of  a  circuit  varies  as  the  square  root 
of  the  product  of  the  inductance  and  capacity,  so  that  doubling  either 
of  these  increases  the  period  by  V2,  i.  e.,  to  1.414  times  its  former 
value.    Doubling  both  inductance  and  capacity  doubles  the  period. 

SELF-INDUCTION. 

129.  We  see  that  all  conductors  must  have  self-induction,  because  we 
know  that  all  currents  are  surrounded  by  magnetic  fields  produced  by 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  81 

the  currents.  The  production  of  the  field  creates  an  E.  M.  F.  in  the 
circuit  opposite  in  direction  to  the  E.  M.  F.  causing  tlie  current  and 
tending  to  stop  it,  so  that  self-induction  has  been  defined  in  a  qualitative 
manner  as  the  inherent  quality  of  electric  currents  which  tends  to  impede 
the  introduction,  variation,  or  extinction  of  an  electric  current  passing 
through  an  electric  circuit. 

It  has  also  been  expressed  in  quantity  as  the  number  of  lines  of  force 
induced  in  a  circuit  by  the  establishment  of  unit  current  in  it.  It  bears 
the  same  relation  to  electricity  as  inertia  does  to  matter;  it  represents 
its  resistance  to  change  of  condition,  and  it  might  be  defined  as  the  work 
necessary  to  create  imit  current  in  a  circuit. 

Suppose  we  wish  to  determine  the  work  done  in  creating  a  current  of 
value  7  in  a  circuit  of  self-induction  L  in  a  time  T. 

Since  L=the  counter  E.  M.  F.  of  self-induction  when  the  current  is 
varied  at  the  rate  of  1  ampere  per  second,  the  counter  E.  M.  F.  when 

it  is  varied  at  the  rate  of  -=-  amperes  per  second  =  ~rn    -     If  ^^^  rise 

in  current  is  uniform,  the  counter  E.  M.  F.  is  uniform  and  the  total 
work  done   (which  equals  the  product  of  the  E.   M.  F.,  current,  and 

time)  would  be  equal  to  -^   xl xT  =  LP,  were  it  not  for  the  fact  that 

the  current  rises  uniformly  from  zero  to  /  and  its  mean  value  is    -^  and 

LP 
therefore  the  work  done=:  ~^-  (4).     Since  the  factor  of  time  does  not 

appear  in  the  result  it  shows  that  it  requires  the  same  amount  of  work 
to  create  a  given  current  in  a  circuit  of  given  self-induction  whether 
it  is  created  slowly  or  quickly,  and  that  this  work  is  equal  in  joules  to 
one-half  the  product  of  the  self-induction  in  henries  by  the  square  of 
the  current  in  amperes.  Therefore  in  a  circuit  whose  self-induction  is 
2  henries  the  work  done  in  creating  a  steady  current  of  10  amperes  is 

equal  to  ^  =100  joules  =73.7  foot-pounds. 

These  73.7  foot-pounds  represent  the  energy  stored  in  the  magnetic 
field;  it  is  the  work  done  by  the  circuit  in  creating  its  own  field.  If  it 
is  in  the  neighborhood  of  other  circuits,  the  momentary  current  created 
in  them  during  the  rise  of  current  reacts  on  the  field  and  makes  the 
amount  of  work  required  still  greater. 

When  the  current  is  broken  the  collapse  of  the  field  restores  this 
energy  to  the  circuit,  thus  tending  to  prolong  the  current. 

In  alternating  currents,  where  the  rise  and  fall  is  continuous,  the 
magnetic  field  is  continually  absorbing  or  giving  out  energy.  In  oscil- 
lating circuits  the  energy  is  constantly  changing  from  magnetic  to 
electric  and  vice  versa. 


83  MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

CAPACITY. 

130.  Now  suppose  we  wish  to  determine  the  work  done  in  charging 
a  condenser  of  capacity  C  to  a  voltage  or  potential  £'  in  a  time  T.  The 
potential  of  the  condenser  is  zero  before  charging  begins  and  increases 
as  the  charge  increases,  so  that  the  resistance  to  charging  also  increases 
with  the  charge;  therefore  it  must  take  more  work  to  add  a  coulomb  of 
electricity  to  a  condenser  of  high  than  to  one  of  low  potential. 

The   total   quantity  of  electricity   in  coulombs  in   the  condenser  is 

Q  =  E  C,  and  assuming  that  the  condenser  is  charged  at  a  uniform  rate, 

CE 
the  coulombs  per  second  flowing  into  it=  _,  ,  and  this  must  equal  the 

amperes  in  the  charging  circuit.  The  condenser  being  charged  at  a 
uniform  rate,  its  potential  will  rise  uniformly  from  zero  to  E  and  the 
total  work  done  during  the  time  T  must  equal  the  average  potential 

4-  Xrate  of  chargextime=  ^X^^  XT  =  ^  (5). 

Since  the  factor  of  time  disappears,  this  shows  that  it  requires  the 
same  amount  of  work  to  charge  a  given  condenser  to  a  given  potential 
whether  it  is  charged  slowly  or  quickly,  and  that  this  work  is  equal  in 
joules  to  one-half  of  the  product  of  the  capacity  in  farads  by  the  square 
of  the  potential  in  volts. 

Therefore,  in  a  circuit  whose  capacity  is  2  farads,  the  work  done  in 

charging  it  to  a  potential  of  10  volts  =  -*-^^^':^  =100  joules  =  73.7  foot- 
pounds. We  see  that  it  takes  the  same  amount  of  work  to  charge  a 
condenser  whose  capacity  is  2  farads  to  a  potential  of  10  volts  as  it 
does  to  create  a  current  of  10  amperes  in  a  circuit  whose  self-induction 
is  2  henries. 

If  the  capacity  of  the  condenser  is  2  microfarads  instead  of  2  farads, 
the  required  work  is  one-millionth  of  73.7  foot-pounds  =  0.0000737  foot- 
pounds. 

These  73.7  foot-pounds  represent  the  energy  stored  in  the  electric  field, 
just  as  the  73.7  foot-pounds  in  art.  129  represented  the  energy  stored  in 
the  magnetic  field. 

Disregarding  losses  it  is  the  amount  of  work  the  condenser  can  do  on 
discharge. 

CONDENSERS  AND  INDUCTANCES   IN   SERIES  AND  IN   PARALLEL. 

131.  When  two  or  more  condensers  are  placed  in  parallel  (fig.  28c), 
their  total  capacity  C  is  equal  to  the  sum  of  their  capacities  taken  singly ; 
i.  e.,  C  =  (7i-fC2-f-etc.    When  two  equal  condensers  are  placed  in  series 


MANUAL   OF    KADIO    TELEGRAPHY   AND   TELEPHONY.  83 

(fig.  28d),  the  resulting  capacity  is  one-half  of  that  of  each  taken  singly, 
or  in  general 

i  =  'k  +  i  +  "''■ 

For  instance,  32  jars  connected  in  2  groups,  with  18  jars  in  parallel  in 
each  group,  would,  if  the  two  groups  were  placed  in  series,  have  a  capacity 
equal  to  only  8  jars  in  parallel. 

Inductances,  however,  follow  the  law  of  resistances.  Two  equal  induc- 
tances in  parallel  have  a  total  inductance  equal  to  half  that  of  each  taken 
singly. 

Or,  when  in  parallel,  -y-  =  ^  +-^  ,  etc.,  whereas  in  series  L=Li-f  L2, 

etc. ;  that  is,  2  or  more  inductances,  in  series,  have  a  total  inductance  equal 
to  the  sum  of  the  individual  inductances. 


Hh 


s 


rHHS    n 


1 3     'A 


Fig.  28c.  Fig.  28u. 


Condensers,  which  will  be  ruptured  if  used  alone,  can  be  used  in  series, 
dividing  the  voltage  between  them.  For  instance,  a  30,000-volt  trans- 
former can  be  used  with  jars,  which  will  stand  but  20,000  volts  by  placing 
2  groups  in  series,  as  in  fig.  28c.  Then  each  jar  will  have  to  stand  but 
15,000  volts. 

132.  We  know  that  by  coiling  a  wire  we  can  increase  its  self-induction 
and,  therefore,  its  electrical  length,  without  any  increase  in  its  physical 
length. 

So  we  add  to  the  self-induction  of  circuits  and,  consequently,  to  their 
periods  of  oscillation,  by  adding  coils  of  wire  in  series,  and  this  is  done 
in  practice  for  both  sending  and  receiving. 

We  can  decrease  their  capacity  and,  consequently,  their  periods  of 
oscillation,  by  adding  condensers  in  series;  but  this  is  usually  done  in 
practice  for  receiving  only. 

If  a  straight  wire  is  broken  in  the  middle,  the  oscillation  period  of  each 
half  would  be  half  of  the  original  period  were  it  not  for  the  fact  that  the 
adjacent  ends  of  the  wire  and  the  air  between  them  form  a  small  condenser, 
which  has  the  effect  of  slightly  increasing  the  capacity  of  each  half,  thus 
giving  it  a  period  slightly  longer  than  half  of  the  original  period. 

It  appears,  therefore,  that  we  can  shorten  the  electrical  length  of  an 
aerial  (fig.  29)  by  putting  a  condenser  in  series  with  it,  but  we  cannot 
shorten  it  to  less  than  one-half  of  its  original  period. 


84  MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

COMBINATION  OF  SELF-INDUCTION   AND   CAPACITY   IN  OSCILLATING 

CIRCUITS. 

133.  In  an  oscillating  circuit,  when  the  condenser  is  discharged — i.  e., 
when  the  coatings  are  at  zero  potential — the  electric  energy  has  been 
transformed  into  magnetic  energy.  If  there  were  no  losses  in  the  con- 
denser due  to  heating,  radiation,  etc.,  the  conversion  would  be  perfect, 
the  work  in  the  magnetic  field  of  the  circuit  referred  to  in  art.  129 
would  equal  73.7  foot-pounds,  and  this,  in  turn,  would  be  again  trans- 
formed into  electric  energy  when  the  condenser  recharges.     (See  art.  54.) 

A  magnetic  field  can  not  be  maintained  steadily  except  by  a  current, 
but  a  condenser  can  be  charged  and  kept  in  that  condition  for  some 
time.  However,  condensers  used  in  wireless  telegraphy  are  always  dis- 
charged immediately,  and  the  energy  stored  in  them  before  discharge  is 
the  stock  in  trade,  so  to  speak,  of  the  sending  apparatus;  it  represents 
the  work  it  can  do  on  the  ether.  This  is  true,  whether  the  capacity  is  con- 
centrated, as  in  a  cundenser,  or  distributed,  as  in  an  aerial. 

CAPACITY    AND    SELF-INDUCTION    OF    STRAIGHT    WIRES. 

134.  The  capacity  and  self-induction  of  all  but  very  simple  forms  of 
circuits  are  very  difficult  to  calculate,  and  in  general  they  are  deter- 
mined by  comparison  with  known  values. 

The  capacity  of  a  straight,  vertical  wire  of  length  I  and  diameter  d,  well 

above  the  earth  and  away  from  other  conductors,  is   C  =  r^yr 

4.1454/0^(1] 

values  being  given  in  centimeters. 

Fleming  states  that  a  wire  111  feet  long  and  diameter  0.085  inch, 
suspended  verticalh^  was  found  to  have  a  capacity  of  0.000205  micro- 
farad, or  approximately  one-tenth  of  one  standard  Leydeu  jar.  Four 
wires  of  the  above  size  and  length,  being  6  feet  apart,  were  found  to  have 
a  capacity  of  0.000583  microfarad,  or  about  three  times  as  much  as  one 
wire. 

One  hundred  and  sixty  such  wires  in  the  shape  of  an  inverted  cone, 
2  feet  apart  at  the  top  and  in  contact  at  the  bottom,  had  a  capacity  of 
only  about  thirteen  times  that  of  a  single  wire. 

It  will  be  seen  that  doubling  the  wire  in  an  aerial  does  not  double  its 
capacity.  For  wires  about  2  feet  apart  the  capacity  increases  approx- 
imately as  the  square  root  of  the  number  of  wires — that  is,  IG  wires 
would  give  four  times  the  capacity  of  1  wire. 

The  self-induction  of  a  straight  wire  of  length  I,  diameter  d,  and  cir- 
cular cross  section,  at  a  distance  from  other  conductors  is  2  I  (2.3026 

log.    —=--1),  values  being  given  in  centimeters.     The  self-induction 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  85 

of  two  parallel  wires  varies  as  the  distance  between  them,  decreasing 
with  the  distance,  so  that  adding  straight  wire  to  an  aerial  does  not  add 
to  its  self-induction  in  the  same  proportion. 

The  relation  between  tlie  inductance  and  capacity  of  a  straight  wire 
of  circular  section  and  diameter  small  in  comparison  with  its  length  is 
such  that  its  electrical  length  is  equal  to  its  natural  length,  and  its  wave 
length  is  therefore  twice  its  natural  length. 

A  vertical  straight  wire,  well  grounded  and  of  small  diameter,  has  an 
apparent  electrical  length  approximately  equal  to  twice  its  natural  length ; 
its  wave  length  is  approximately  four  times  its  natural  length. 

Pierce  states  that  a  single  wire  100  feet  long  and  ^  inch  diameter, 
when  alone  in  space,  has  as  much  capacity  as  an  isolated  flat  metallic  ditc 
16  feet  in  diameter.* 

TIME  CONSTANTS  OF  CONDENSERS  AND  INDUCTIVE  CIRCUITS. 

135.  Every  capacity  and  inductance  has  what  is  called  its  time  constant. 
The  time  constant  of  a  condenser  is  equal  to  C  R — i.  e.,  the  product 

of  its  capacity  and  the  resistance  through  which  it  is  charged.  If  C  is 
measured  in  microfarads,  R  must  be  measured  in  megohms,  and  their 
product  will  then  be  in  seconds.  The  greater  the  time  constant  of  a 
condenser  the  longer  time  it  will  take  for  it  to  arrive  at  a  given  fraction 
of  the  charging  potential. 

For  any  usual  transformer  charging  frequency  this  effect  is  inappre- 
ciable. 

The  time  constant  of  an  inductive  circuit  =  ^^ .    The  greater  the  time 

K 

constant  of  a  circuit  the  longer  it  takes  to  establish  a  current  of  a  given 

strength  in  it  (art.  30). 

DIFFERENCE  BETWEEN  DIRECT  AND  ALTERNATING  CURRENTS  DUE  TO  SELF- 
INDUCTION   AND   CAPACITY. 
E 

136.  The  fundamental  electric  equation  7=    ^^s  derived  from  meas- 

xt 

urements  of  the  relations  existing  between  electric  current  and  a  con- 
stant E.  M.  F.  in  a  circuit  of  constant  resistance. 

Self-induction  only  affects  a  current  when  it  is  being  started  or 
stopped.  It  increases  the  time  it  takes  for  the  current  to  rise  to  its 
steady  value  and  the  time  it  takes  to  fall  to  zero.  For  continually 
changing  currents  both  in  strength  and  direction  it  impedes  both  rise 
and  fall,  and  therefore  acts  as  a  resistance,  so  that  the  resistance  of  a 
circuit  for  alternating  currents  is  not  the  same  as  for  steady  or  direct 
currents,  but  is  a  combination  of  the  ohmic  resistance  and  the  induc- 

•  Principles  of  Wireless  Telegraphy,  by  G.  W.  Pierce,  A.M.,  Ph.D.   (1910). 


86  MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHGNT. 

tive  resistance  or  reactance  (art.  30).  Reactance  is  not  a  true  ohmic 
resistance,  which  appears  as  heat,  but  is  rather  a  counter  or  opposing 
E.  M.  F. 

The  action  is  still  further  complicated  in  circuits  having  capacity, 
as  wireless  telegraph  circuits  have,  since  capacity  is  found  to  assist  both 
the  rise  and  fall  of  current,  and  therefore  to  act  in  an  opposite  direction 
to  the  self-induction  and  to  decrease  the  total  resistance  or  impedance. 

In  alternating  circuits  we  have  /=     ~  where  Z  =i\\Q  impedance  = 

Zi 

J  'B?-\-     2nNL ^  N  being  the  frequency  of  the  alternating 

current. 

Since    capacity   and   inductance   produce    opposite    effects,   they   can 

be  used  to  neutralize  each  other.    If  2ttNL=  o-nP  ^^^^  equation  becomes 

7=  -^  as  for  direct  currents,  E  being  the  instantaneous  value  of  the 

E.  M.  F. 

In  circuits  where  the  resistance  and  capacity  are  very  small,  and  the 
self-induction  comparatively  large,  as  in  primaiy  sending  circuits, 
2r  =  approximately  27rNL,  or  the  current  depends  almost  entirely  on  the 
reactance  of  self-induction.  The  current  in  wireless  telegraph  sending 
circuits  is  sometimes  governed  by  reactance  regulators  placed  in  the 
primary  circuit.     (See  art.  30.) 

137.  The  equation  P  =  IE(2)  is  also  derived  from  the  relations  existing 
between  power,  current  and  E.  M.  F.  in  direct  current  circuits. 

In  alternating  current  circuits,  the  current  and  E.  M.  F.  due  to  the 
effect  of  self-induction  and  capacity  do  not  reach  their  highest  and  lowest 
points  together  except  when  as  pointed  out  in  the  preceding  article, 

27rNL=-     ,-,^.     The  release  of  energy  stored  in  an  inductance  creates 
2TrNC  -^ 

a  current  in  the  same  direction  as  the  inducing  current.  The  release  of 
energy  stored  in  a  capacity  creates  a  current  in  the  opposite  direction  to 
the  charging  current.  Inductance  in  a  circuit,  therefore,  delays  the 
reversal  of  a  current;  i.  e.,  causes  the  change  to  lag  behind  the  electro- 
motive force  which  produces  it.  Capacity  on  the  other  hand,  assists  the 
reversal  of  a  current;  i.  e.,  it  produces  a  leading  current,  or  one  which 
is  ahead  of  the  electro-motive  force  which  produces  it. 

Since  the  power  at  any  instant  is  equal  to  the  current  at  that  instant, 
multiplied  by  the  E.  ]\I.  F.  at  the  same  instant,  the  product  of  the  readings 
of  the  A.  C.  voltmeter  and  ammeter  in  such  a  circuit  does  not  give  the  true 
power  expended  in  the  circuit,  but  only  the  apparent  power.  The  true 
power  can  generally  only  be  obtained  by  the  use  of  a  wattmeter,  which  auto- 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  87 

matically  multiplies  the  instantaneous  values  of  voltage  and  current  and 
indicates  the  product. 

The  ratio  of  the  true  power  to  the  apparent  power  is  called  the  powei 
factor. 

SKIN  EFFECT  IN  HIGH-FREQUENCY  ALTERNATING  CURRENTS. 

138.  Another  effect  of  alternating  currents  on  the  apparent  resistance 
of  circuits  is  seen  when  the  frequencies  are  above  100.  It  is  called  by 
Fleming  the  phenomenon  of  skin  or  surface  resistance.  The  current 
seems  to  begin  at  the  surface  of  a  conductor  and  soak  in,  and  to  penetrate 
to  the  center  it  must  have  time.  This  is  another  instance  of  the  time 
effect  that  must  be  kept  in  mind  when  dealing  with  alternating  and  oscil- 
lating currents. 

If  the  wire  is  of  iron  its  comparative  increase  resistance  for  high-fre- 
quency currents  is  still  greater  than  that  of  non-magnetic  wire. 

The  resistance  of  No.  16  wire  for  frequencies  of  a  million  is  6.5  times 
greater  than  its  steady  resistance.  The  larger  the  diameter  of  the  wire 
the  greater  the  proportional  increase  in  resistance.  Stranded  wire, 
having  proportionally  greater  surface  than  solid  wire  of  the  same  area 
of  cross  section,  offers  less  resistance  to  high-frequency  currents. 

Flat  ribbons,  having  larger  surface,  offer  less  resistance  than  circular 
wire  of  the  same  area  of  cross  section. 

In  the  Stone  receiving  circuits,  the  inductance  coils  were  wound  with 
wire  of  such  size  that,  for  the  frequency  intended,  the  current  penetrated 
to  the  center  and  there  was  no  wasted  material.  Resistance  is  decreased 
by  using  a  number  of  strands  in  parallel.  Fleming  advocates  this  for  send- 
ing circuits,  and  Marconi  uses  very  heavy  stranded  wire  for  inductances 
at  high-powered  stations. 

Currents  in  wireless  telegraph  circuits  having  a  wave  length  of  300 
meters  penetrate  about  yV  millimeter,  or  approximately  ^^  inch,  inside 
the  surface  of  the  conductor.  If  the  wires  are  of  iron  the  current  pene- 
trates about  -j-j^^^^inch. 

139.  We  see,  therefore,  that  in  wireless  telegraph  circuits  the  resistance 
is  not  a  constant,  but  depends  on  the  frequency,  i.  e.,  on  the  wave  length 
we  are  using.  Generally  speaking,  the  shorter  the  wave  length  the  greater 
the  resistance,  though  we  have  actually  less  length  of  wire. 

Dr.  Austin  has  shown  that  for  grounded  circuits,  such  as  aerials,  there  is 
a  point  where  the  resistance  is  lowest  and  an  increase  or  decrease  in  wave 
length  will  increase  the  resistance. 

He  finds  that  resistance  varies  nearly  inversely  as  the  square  of  the  wave 
length  up  to  a  point  which  is  slightly  less  than  twice  the  natural  wave 
length  of  the  aerial.    Beyond  this  point  the  resistance  rises  again  nearly 


88  MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

in  direct  proportion  to  the  wave  length.  This  rise  in  resistance  appears 
to  be  less  on  ships,  where  there  is  good  ground,  than  on  shore,  where  the 
ground  is  comparatively  not  as  good. 

For  instance,  the  aerial  at  the  Bureau  of  Standards  had  a  resistance  of 
32  ohms  for  wave  lengths  of  400  and  2000  meters,  while  its  resistance  for  a 
wave  length  of  650  meters  was  about  12  ohms. 

In  the  case  of  a  ship,  the  Maine's  aerial  had  a  resistance  of  10  ohms  for 
a  400-meter  wave.  A  resistance  of  less  than  5  ohms,  for  a  500-meter  wave, 
and  a  resistance  of  but  little  more  than  2  ohms  for  a  750-meter  wave. 

For  inductances  such  as  are  used  in  closed  sending  circuits  and  in 
receiving  circuits  he  found  that  the  resistance  also  varies  inversely  as  the 
wave  length. 

For  very  long  wave  lengths  and  small  coils  the  resistance  was  not  much 
greater  than  the  direct  current  resistance,  but  generally  the  high  frequency 
resistance  increased  faster  than  the  number  of  turns  of  the  coil,  but  not  as 
fast  as  the  self-induction,  i.  e.,  the  self-induction  of  a  circuit  can  be  in- 
creased without  increasing  its  high  frequency  resistance  in  the  same 
proportion. 

MEASUREMENT  OF  INDUCTANCE  AND  CAPACITY  IN  OSCILLATING  CIRCUITS. 

140.  By  comparison  with  standard  inductances  and  capacities,  the 
capacity  and  self-induction  of  circuits  can  be  measured  and  their  periods 
calculated. 

Measured  inductances  and  capacities  connected  together  so  as  to  form 
an  oscillating  circuit  are  made  so  that  the  capacity  or  inductance  (usually 
the  capacity)  or  both  are  variable.  They  can  be  calibrated  so  as  to  show 
directly  either  the  period  or  wave  length  of  the  circuit  for  any  position  of 
the  variable  elements. 

If  brought  near  another  circuit  in  which  electrical  oscillations  are 
taking  place  and  adjusted  so  as  to  have  a  maximum  of  current  induced 
the  two  circuits  are  said  to  be  in  tune  or  resonance.  (They  have  the 
same  electrical  length.)  When  used  as  above,  calibrated  oscillating  cir- 
cuits are  called  wave  meters,  ondameters  or  cymometers. 

Wave  meters  can  be  so  arranged  as  to  measure  separately  the  induc- 
tance or  capacity  of  oscillating  circuits  as  well  as  their  periods.  If  a 
spark  gap  forms  part  of  the  oscillating  circuit,  its  period  can  also  be 
directly  measured  by  measuring  the  time  between  the  successive  surgings 
of  the  spark.  This  is  done  by  photographing  the  sparks  by  reflection 
from  the  surface  of  a  rapidly  revolving  mirror.  The  movement  of  the 
mirror  between  sparks  separates  their  images  on  the  photographic  film, 
and  knowing  the  number  of  revolutions  of  the  mirror  per  second,  the 
elapsed  time  between  sparks  can  be  calculated  and  hence  the  period  of  the 
circuit. 


Chapter  V. 

POWER  EXPENDITUEE  AND  EFFICIENCY  OF  SENDING  AND 
EECEIVING  APPARATUS. 

141.  With  a  given  power  the  work  that  can  be  done  per  second  is  fixed 

(JVJ2 

In  charging  a  condenser  TF=  ___(5) .     The  number  of  times  this  is  done 

per  second  gives  the  work  per  second,  or  the  'power  expended.  By 
increasing  the  frequency  we  can  for  a  given  power  either  reduce  the 
voltage  (length  of  gap)  or  the  capacity  of  the  condenser.  For  instance, 
at  a  frequency  of  500  cycles,  for  the  same  power,  the  condenser  need  only  be 
1/10  the  size  of  that  for  a  frequency  of  50  cycles.  Or,  keeping  the  capacity 
the  same,  the  voltage  can  be  reduced  to  1/V 10  =  approximately  1/3  of 
that  necessary  for  the  same  power  at  50  cycles.  A  table  showing  the 
capacities  necessary  for  given  powers  at  different  frequencies  and  voltages 
is  given  in  table  2,  appendix  A. 

MECHANICAL    WORK   DONE   IN    MAKING    DOTS   AND   DASHES   OF   THE   TELE 

GRAPH  CODE. 

142.  We  are  now  in  position  to  speak  in  more  specific  terms  of  the 
work  done  in  sending  wireless  telegrams. 

Let  us  suppose  that  we  are  delivering  2  kilowatts  at  60  cycles  and 
110  volts  to  a  transformer,  which  delivers  it  to  a  condenser  at  a  maxi- 
mum potential  of  30,000  volts. 

Two  kilowatts  =2000  watts  =  2000  joules  per  second  =  1474  foot-pounds 
per  second. 

Since  60  cycles=120  alternations  per  second,  the  work  equals  approxi- 
mately 12.3  foot-pounds  per  alternation. 

If  the  work  done  on  the  condenser  is  in  phase  with  the  charging 
E.  M.  F.,  and  if  the  spark  gap  is  set  to  break  down  at  a  potential  of 
30,000  volts,  the  condenser  will  be  discharged  at  the  peak  of  the  charging 
curve,  or  when  one-half  of  the  work  that  can  be  done  in  an  alternation 
(12.3  foot-pounds)  has  been  done  on  the  condenser.  The  capacity  of  a 
condenser  which  takes  12.3  foot-pounds  of  work  to  charge  it  to  30,000 
vclts  =  .0372  microfarad,  or  approximately  eighteen  0.002  microfarad 
jars. 

Suppose  we  are  sending  at  the  rate  of  20  words  per  minute,  that  the 
words  average  5  letters  each,  and  that  each  letter  is  made  up  of  3  char- 
acters equal  in  length  to  9  dots,  then  a  minute  can  be  represented  as 
equal  to  20x5x9  =  900  dots=15   dots  per  second.     In  other  words, 


90  MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

the  length  of  a  dot  is  one-fifteenth  of  a  second.  Now  we  have  120  alter- 
nations per  second,  so  that  we  have  about  8  alternations  per  dot  when 
sending  at  the  rate  of  20  words  per  minute;  therefore  a  dot  is  made  up  of 
8  distinct  sets  of  discharges  of  the  condenser  and  a  dash  of  three  times 
that  number.  The  condenser  is  doing  work  in  producing  ether  waves  at 
the  rate  of  12.3  foot-pounds  per  alternation,  equaling,  approximately,  100 
foot-pounds  per  dot  and  300  foot-pounds  per  dash. 

It  will  be  noted  from  the  text  that  at  this  sending  rate  the  frequency 
necessary  to  give  1  alternation  per  dot  and  2  alternations  per  dash  is  only 
7^  cycles  per  second. 

It  will  be  noted  further  that  with  one  spark  per  alternation  we  cannot 
utilize  2  kilowatts  continuously.  We  can  only  use  it  in  charging  the  con- 
denser during  the  first  half  of  each  alternation.  As  soon  as  the  discharge 
begins  the  condenser  circuit  oscillates  in  its  own  period  as  if  entirely 
disconnected  from  the  transformer. 

In  this  respect  the  charge  and  discharge  of  a  condenser  resembles  the 
loading  and  firing  of  a  gun. 

143.  Professor  G.  W.  Pierce,  of  Harvard  University,  has  measured  tht 
period  of  some  types  of  oscillating  circuits  used  in  wireless  telegraphy, 
and  it  is  from  his  published  account  of  his  experiments  that  the  follow- 
ing description  is  derived. 

Suppose  a  spark  gap  set  to  break  down  at  a  potential  of  10,000  volts,, 
to  be  used  in  a  circuit  where  the  maximum  potential  reached  in  the 
condenser  is  30,000  volts. 

Let  the  curve  of  sines  in  fig.  18  represent  the  condenser  potentials: 
of  the  oscillating  circuit  during  2  alternations,  each  lasting  y^s  of  a 
second. 

The  resistance  of  the  spark  gap  is  practically  infinite  before  the  poten- 
tial reaches  10,000  volts,  and  therefore  no  current  passes.  When  the 
potential  has  risen  to  10,000  volts  the  spark  gap  is  ruptured.  Its  resist- 
ance decreases  instantly  to  a  fraction  of  an  ohm,  and  during  the  first 
half  of  the  oscillation  the  condenser  is  discharged  to  zero  potential.  Dur- 
ing the  last  half  of  the  oscillation  it  is  charged  again  in  the  opposite 
sense.  The  sparks  pass  first  in  one  direction  and  then  in  the  other,  and 
the  spark  gap  not  regaining  its  resisting  qualities,  the  oscillations  or 
surgings  continue  until  the  potential  (owing  to  losses  due  to  the  radiation 
of  energy  in  the  shape  of  electric  waves,  to  heating  the  circuit,  and  the 
light  and  heat  at  the  spark  gap)  does  not  rise  high  enough  to  disrupt 
the  gap. 

The  transformer  Immediately  recharges  the  condenser,  which,  as  soon 
as  it  again  reaches  a  potential  of  10,000  volts,  breaks  down  the  spark  gap 
again,  and  a  second  series  of  oscillations  begins. 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  91 

In  the  circuit  under  consideration  the  maximum  charging  potential 
is  30,000  volts,  so  that  a  condenser  with  a  spark  gap  breaking  down  at 
10,000  volts  may  be  charged  and  discharged  several  times  during  one- 
half  cycle  of  the  charging  current. 

The  spark  acts  like  a  trigger  which  suddenly  releases  the  stored 
energy  in  the  condenser,  and  as  soon  as  this  energy  has  been  radiated, 
the  trigger  automatically  resets  itself  and  does  not  release  again  until 
the  condenser  is  recharged. 

It  is  evident  that  if  the  spark  gap  in  the  circuit  under  consideration 
is  adjusted  to  30,000  volts,  but  one  discharge  of  the  condenser  per  alterna- 
tion will  take  place  and  but  one  train  of  waves  will  be  sent  out.  Shorten- 
ing the  gap  will  increase  the  number  of  discharges  per  alternation. 

The  exact  number  for  any  spark-gap  length  will  depend  on  the  time 
of  an  alternation — i.  e.,  the  frequency,  and  on  the  length  of  time  it  takes 
the  available  power  to  charge  the  condenser  to  the  voltage  required  to 
break  down  the  gap.  Less  energy  per  wave  train  will  be  radiated  on  a 
short  gap  than  on  a  long  one,  because  the  work  done  varies  as  the  square 
of  the  voltage  (see  art.  130)  ;  but  the  total  work  done  may  be  equal,  on 
account  of  the  greater  number  of  discharges. 

If  the  spark  gap  is  too  short,  an  arc  is  formed  and  no  oscillations  take 
place  except  those  due  to  the  frequency  of  the  charging  current. 

Professor  Pierce  has  shown  that  the  interval  between  wave  trains  may 

vary  on  account  of  the  residual  charge  left  in  the  condenser.    When  the 

spark  gap's  original  resistance  is  restored,  the  potential  of  the  residual 

charge  may  be  opposed  to  the  potential  of  the  transformer  and  delay  the 

charging.     He  has  shown  also  that  the  gap  sometimes  partly  retains  its 

conducting  character  and  breaks  down  at  a  lower  potential  than  its  length 

would  indicate.     This  makes  the  sparks  and  oscillations  irregular  in 

strength  and  number  and  produces  ragged  and  poor  signals. 

E 
144.  Keeping  in  mind  our  five  equations — /=    „    (1);  P~IE   (2): 

period  (T)  =2^VLC  (3)  ;  1F= -^  (4) ;  and  W=  ^^'' (5). 

Let  us  consider  a  condenser  having  a  capacity  of  0.02  microfarad 
(10  standard  jars  in  parallel)  charged  to  a  potential  of  30,000  volts. 

Such  a  condenser  would  contain  ynTYT^-fnyf-v  =0.0006  coulomb,  and 

1,  ,             ^^       f  A  ■             1            i^2X  10«X  9X  10»      o    .     , 
would  be  capable  of  domg  work  equal  to ^ =9  joules 

=  6.64  foot-pounds. 

If  this  condenser  is  discharged  through  a  circuit  having  a  self-induc- 
tion of  such  value  (0.00125  millihenry)  as  will  give  a  wave  length  of 
300  meters,  the  frequency  of  the  circuit  is  1,000,000,  the  alternations 
2,000,000  per  second,  and  0.0006  coulomb  will  create  in  such  a  circuit 


92  MANUAL   OF   RADIO    TELEGRAPHY   AND   TELEPHONY. 

a  momentary  current  having  an  effective  value  of  approximately  2700 
amperes.* 

If  this  energy  is  radiated  in  five  complete  oscillations,  the  rate  of 
doing  work,  if  the  efficiency  of  conversion  is  unity,  is  9  joules  in  Tu-olTr¥f 
second  =1,800,000  per  second  =  1800  kilowatts. 

This  shows  that  though  the  available  energy  is  very  small,  the  rate  of 
doing  work,  that  is,  the  power  of  a  wireless  telegraph  sender,  may  be 
very  great  for  an  exceedingly  short  period  of  time. 

145.  Let  us  now  consider  the  case  of  continuous  oscillations. 

The  Elaine's  aerial,  mentioned  in  art.  139,  had  a  capacity  of  ,001  mf.. 
half  of  one  standard  jar. 

Considered  as  a  condenser,  charged  to  1000  volts,  it  would  contain 
.000001  coulomb,  which  would  create  in  a  circuit  of  a  frequency  of 
1,000,000  (i.  e.,  2,000,000  alternations)  a  momentary,  effective  current 
of  approximately  four  amperes. 

If  this  energy  is  radiated  in  five  complete  oscillations,  the  rate  of  doing 
work  (that  is,  the  power)  is  equal  to  .1  k.  w. 
E 


A^ 


When  oscillating,  the  potential  of  the  charge  in  the  Maine's  aerial,  at 
tho  instant  of  reversal  of  the  current,  might  be  represented  by  the  line 
E  C,  fig.  18e.  The  point  C,  being  the  ground  at  zero  potential,  the 
point  A  being  the  upper  end  of  the  aerial  at  the  maximum  potential. 

The  total  charge  in  the  aerial  will  be  its  capacity  multiplied  by  the  mean 
potential  from  C  to  A,  The  total  work  it  can  perform  will  be  its  capacity 
multiplied  by  one-half  the  mean  of  the  squares  of  the  potentials  from  C 
to  A.    Suppose  this  mean  square  is  10000^,  then  this  aerial  in  dissipating 

*  Statement  in  preceding  editions  of  this  book,  that  the  momentary  current 
in  such  a  case  is  1200  amperes,  was  based  on  the  average  coulombs  passing  a 
given  point  in  a  half-cycle,  and  was  incorrect.  It  was  intended  to  show  the 
necessity  for  large  surface  area  in  inductances  of  radio  sets.  At  high-powered 
stations,  Marconi  installs  condenser  leads  and  inductances  with  very  large 
surfaces.  For  low-powered  stations,  however,  no  such  provision  is  made.  But 
losses  from  small  wires  may  be  greater  than  we  perceive,  since  recent  experi- 
ments by  Alexanderson  have  shown  that  corona  losses  may  begin  as  low  as 
3000  volts,  and  he  dissipated  one-half  kilowatt  in  two  wires,  each  y*o -millimeter 
diameter,  1  meter  long,  in  air,  at  a  distance  apart  of  two  feet  Difference  of 
potential,  2700  volts;  frequency  100,000  cycles.  The  wires  did  not  heat,  but 
were  surrounded  by  the  blue  flame  of  the  corona. 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  93 

such  a  charge  would  do  work  at  the  rate  of  10  K.  W.  on  a  maximum  voltage 
of  about  14,000  volts.  If  the  energy  is  supplied  as  fast  as  it  is  dissipated, 
the  rate  of  doing  work  will  be  greater  than  10  Iv.  W.,  because  the  amount 
of  work  done  during  the  first  oscillation  is  greater  than  during  any  suc- 
ceeding oscillation. 

This  is  due  to  the  fact  stated  in  art.  100,  that,  with  damped  oscillations, 
the  amplitude  of  each  oscillation  is  a  given  fraction  of  the  one  preceding 
it  and  to  the  fact  that  the  work  done  varies  as  the  square  of  the  amplitude. 

For  instance,  suppose  the  first  oscillation  has  an  amplitude  of  10  and  the 
next  of  8;  the  fraction  is  j-^  and  the  third  oscillation  has  an  amplitude  of 
6.4.  The  work  done  is  as  the  squares  of  the  amplitudes,  or  as  100  to  64  to 
40.96,  etc.  From  which  it  will  be  seen  that  36  per  cent  (100-64)  of  the 
total  work  is  done  during  the  first  complete  oscillation,  about  23  per  cent 
(64-40.96)  during  the  second,  and  so  on. 

146.  From  the  foregoing  we  see  that  if  we  know  the  capacity  of  an  aerial, 
its  damping,  its  maximum  potential  and  its  frequency,  we  can  determine 
very  closely  the  amount  of  power  dissipated  by  it,  if  it  is  oscillating 
continuously. 

If  oscillating  intermittently,  we  must  know  also  the  frequency  of  tlie 
source  of  supply. 

Standard  methods  of  measuring  all  of  these  quantities,  except  the 
maximum  potential,  have  been  developed. 

EFFICIENCY  OF  SENDING  APPARATUS. 

147.  On  account  of  unavoidable  losses,  we  cannot  supply  to  the  aerial 
all  of  the  energy  supplied  by  the  transformer,  nor  all  of  that  stored  in  the 
condenser. 

With  a  certain  wireless  telegraph  set,  on  which  experimental  measure- 
ments were  made,  Fleming  found  the  actual  power  radiated  to  be  about  10 
per  cent  of  that  supplied  to  the  transformer  and  20  per  cent  of  that  sup- 
plied to  the  condenser.* 

The  arc  set  is  roughly  15  per  cent  efficient,  over-all,  on  powers  below 
20  K.  W.,  and  50-60  per  cent  efficient  for  sets  between  50  and  100  Iv.  W. 

Professor  Fessenden  and  Dr.  L.  W.  Austin,  in  the  Brant  Eock  experi- 
ments, found  that,  with  the  set  on  which  measurements  were  made,  about 
75  per  cent  of  the  power  delivered  to  the  spark  gap  was  given  to  the  aerial. 
Other  experiments  have  shown  that  80  per  cent  to  90  per  cent  of  the  energy 
delivered  to  the  transformer  is  transferred  to  the  closed  circuit. 

We  may  conclude  that  60  per  cent  (80x75)  is  a  fair  over-all  efficiency 
for  a  wireless  set,  i.  e.,  60  per  cent  is  delivered  to  the  aerial,  where  it  is 
dissipated  partly  in  heat  and  partly  in  radiating  electric  waves.  As  yet 
we  have  no  standard  means  of  separating  these  two  factors. 

*Journal  Institution  of  Electrical  Engineers,  vol.  44,  London,  April,  1910. 


94  MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

Very  few  complete  investigations  of  the  efficiency  of  wireless  telegraph 
sets  have  been  made.* 

LOSSES  IN  CONDENSERS. 

148.  When  a  piece  of  iron  is  magnetized  and  demagnetized — i.  e.,  goes 
through  a  cycle  of  magnetization — a  certain  amount  of  energy  is  ex- 
pended, which  appears  in  the  shape  of  heat  in  the  iron.  It  is  supposed 
to  be  due  to  internal  friction  in  the  molecules  of  the  iron  and  is  called 
magnetic  hysteresis. 

In  the  same  way,  to  put  a  condenser  through  a  cycle  of  charge  and 
discharge  requires  the  expenditure  of  a  certain  amount  of  energy,  which 
appears  as  heat  in  the  dielectric  and  is  called  dielectric  hysteresis.  The 
loss  of  energy  due  to  this  quality  varies  in  different  dielectrics  and  is  a 
function  of  the  frequency. 

In  choosing  condensers  for  the  closed  sending  circuit,  it  is  of  great 
importance  to  find  those  which  will  absorb  a  minimum  of  energy  and  at 
the  same  time  show  no  tendency  to  break  down  under  the  large  differ- 
ences of  potential  impressed  upon  them. 

The  losses  of  energy  in  condensers  are  of  two  kinds :  internal  losses 
produced  by  dielectric  hysteresis,  and  external  losses  produced  by  the 
brush  discharges  at  the  edges  of  the  conducting  surfaces.  The  ideal 
dielectric  in  respect  to  the  internal  losses  is  air,  as  it  is  entirely  free  from 
internal  energy  absorption.  When  used  at  ordinary  pressures,  however, 
it  is  unable  to  bear  any  considerable  difference  of  potential.  It  has  been 
discovered  that  when  the  air  pressure  is  increased  to  tlie  neighborhood  of 
250  pounds,  the  dielectric  strength  becomes  so  great  that  it  is  suitable  for 
use  at  any  of  the  potentials  ordinarily  used  in  wireless  telegraphy. 
Compressed  air  condensers  are  ordinarily  made  up  in  the  form  of  a  series 
of  plates  so  connected  that  the  alternate  plates  may  be  charged  positively 
and  negatively,  and  the  whole  set  is  enclosed  in  an  air-tight  steel  tank 
which  can  be  pumped  up  to  the  desired  pressure.  Such  a  condenser, 
while  ideal  in  its  electrical  properties,  is  somewhat  bulky,  and  difficulties 
are  sometimes  found  in  preventing  leakage  of  the  air.  It  is  therefore 
common  in  stations,  where  the  last  degree  of  efficiency  is  not  demanded,  to 
make  use  of  glass  condensers,  in  the  form  of  either  flat  plates  or  jars. 
The  conducting  surfaces  of  condensers  are  now  generally  formed  of  elec- 
trolytically  deposited  copper.  It  is  generally  stated  that  flint  glass  is  the 
glass  best  suited  to  form  the  dielectric.     Experiments  which  have  been 

*  At  Tuckerton,  N.  J.,  the  antenna  resistance,  at  7400-meter  wave  length,  is 
6  ohms.  Tlie  Goldschmidt  high-frequency  alternator  produces  135  amperes  in 
the  antenna,  with  an  input  of  180  K.  W.,  which  on  a  CT'R  basis  gives  an  overall 
efficiency  of  60  per  cent.  At  the  same  station,  an  arc  set  with  an  input  of 
approximately  90  K.  W.,  produces  approximately  the  same  antenna  current, 
with  an  apparent  antenna  resistance  of  only  3  ohms. 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  95 

made  show  that  the  internal  losses  of  glass  condensers  in  ordinary  use 
amount  to  from  2  to  8  per  cent  of  the  total  energy  flowing  through  them. 
The  losses  due  to  the  brush  discharges  from  the  edges  of  the  conduct- 
ing surfaces,  which  sometimes  amount  to  30  per  cent  of  the  total  energy, 
may  be  much  reduced  by  immersing  tlie  condensers  in  oil  or  by  placing 
several  condensers  in  series,  which  reduces  the  individual  potential  differ- 
ence on  each  condenser,  or  by  covering  edges  of  foil  (or  copper)  and 
plates  with  an  insulating  compound. 

149.  Dr.  Austin  has  measured  the  losses  in  various  types  of  sending 
condensers  and  expresses  the  total  losses  as  an  equivalent  resistance.  He 
summarizes  his  results  as  follows : 

1.  The  losses,  in  the  compressed  air  condenser  used,  amount,  at  a  pres- 
sure of  15  atmospheres,  to  an  equivalent  resistance  of  between  0.1  and  0.2 
ohms. 

2.  Condensers  in  which  brushing  is  prevented  by  the  nature  of  their  con- 
struction show  no  change  in  resistance  between  the  limits  of  observation, 
4000  to  20,000  volts,  indicating  that  the  internal  losses  are  independent 
of  voltage. 

3.  Leyden  jars  of  commercial  types  immersed  wholly  in  oil  show  losses 
but  slightly  greater  than  those  of  the  compressed-air  condenser. 

4.  The  paper  and  micanite  condensers  measured  show  very  much  larger 
losses. 

5.  The  resistances  of  the  different  Leyden  jars  in  air  increase  greatly 
over  resistances  when  measured  in  oil,  and  vary  between  1  and  1.8  ohms 
at  14,500  volts.  Between  10,000  and  20,000  volts  the  equivalent  resist- 
ance increases  approximately  in  proportion  to  the  square  of  the  voltage. 

6.  Placing  Leyden  jars  in  parallel  series,  the  capacity  remaining  the 
same,  does  not  diminish  their  brushing  losses  below  20,000  volts. 

7.  Immersing  only  the  edges  of  the  conducting  coatings  of  Leyden  jars 
in  oil  gives  an  equivalent  resistance  midway  between  that  observed  when 
wholly  in  air  or  wholly  in  oil. 

8.  Brushing  losses  are  much  increased  by  any  semiconducting  material 
on  the  surface  of  the  glass  at  the  edges  of  the  conducting  coatings  of 
Leyden  jars. 

9.  The  resistance  of  condensers  increases  nearly  in  proportion  to 
the  wave  length. 

10.  The  losses  in  mica  condensers,  using  carefully  selected  mica,  are  con- 
siderably less  than  in  glass-jar  condensers. 

LOSSES  IN  CLOSED  AND  OPEN  CIRCUITS. 

150.  The  losses  in  the  closed  circuit  inductance  are  those  due  to  its 
high-frequency  resistance  (art.  138).  To  these  we  must  add  losses  from 
the  sound,  light,  and  heat  in  the  spark  gap.  Of  these,  the  heat  losses  are 
considerable,  as  is  shown  by  the  necessity  of  using  blowers  for  preventing 


96  MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONT. 

arcing  in  spark  sets  and  in  the  necessity  for  water  cooling  the  electrodes 
in  arc  sets.  In  arc  sets,  a  non-inductive  resistance,  called  a  dead  or  ballast 
resistance  (fig.  29d),  must  be  used  to  steady  the  arc  and  this  is  an  addi- 
tional source  of  loss. 

While,  as  previously  stated,  a  closed  circuit  is  a  persistent  oscillator 
and,  therefore,  a  poor  radiator,  it  does  radiate  some  energy,  and  this  is  an 
additional  loss,  since  the  radiation  from  the  closed  circuit  is  not  useful. 

151.  Losses  in  the  open  circuit  are  discussed  in  art.  147.  We  want  the 
useful  losses — those  due  to  radiation — to  be  as  large  as  possible.  The 
faster  the  aerial  radiates  energy,  in  the  form  of  electric  waves,  the  less  the 
loss  in  heat  and  the  more  efficient  it  is  as  a  wave  producer.  But  unless 
its  oscillations  are  persistent  enough  to  permit  selective  tuning  of  receiver 
circuits,  it  is  a  detriment  to  carrying  on  communication.  We  are,  for  this 
reason,  restricted  in  spark  sets  to  a  certain  limit  of  persistency,  i.  e.,  the 
damping  of  the  oscillations  must  not  exceed  a  certain  limit,  which  is  ex- 
pressed in  the  law  (appendix  D)  as  follows :  "  The  logarithmic  decrement 
per  complete  oscillation  in  the  wave  trains  emitted  by  the  transmitter  shall 
not  exceed  two-tenths,  except  when  sending  distress  signals." 

If  successive  values  of  the  amplitude  of  damped  oscillations  are  meas- 
ured and  their  relative  values  expressed  in  figures,  the  natural  logarithms* 
of  these  figures  will  differ  by  a  constant  quantity  called  the  decrement  and 
it  is  this  constant  difference  which  it  is  specified  by  law  shall  not  exceed  .2. 
A  decrement  of  .2  gives  about  15  complete  oscillations  before  the  amplitude 
falls  to  yV  of  the  maximum  and  permits  good  tuning. 

152.  Of  course  continuous  oscillations  permit  much  more  selective  tun- 
ing, because  we  can  get  along  fairly  well  with  only  15  oscillations  in  y^Vo 
of  a  second,  while  we  would  have  300  oscillations  in  the  same  length  of 
time  if  they  were  continuous  and  we  were  sending  a  1000-meter  wave. 

A  large  decrement  in  an  open  circuit,  used  for  continuous  oscillations, 
is,  therefore,  not  a  defect;  in  fact,  it  serves  to  increase  efficiency  if  its 
cause  is  rapid  radiation  and  not  high  resistance. 

A  whip-crack  transmitter,  which  is  not  permissible  with  spark  sets,  is 
all  right  for  arc  or  other  apparatus  producing  continuous  oscillations. 

RELATION  BETWEEN  HEIGHT  OF  AERIAL,  OSCILLATING  CURRENT,  WAVE 
LENGTH  AND  DISTANCE  OF  TRANSMISSION. 

153.  From  the  results  of  experiments  made  at  Brant  Eock  in  1909-1910, 
Dr.  Austin  has  expressed  the  relation  between  the  vertical  height  of  the 

*  The  logarithm  of  a  number  is  the  power  to  which  another  number  called 
the  base  must  be  raised  to  equal  the  number  in  question.  For  instance  the 
logarithm  of  100  to  the  base  10  is  2  because  10  must  be  squared  to  equal  100. 
The  base  of  so-called  natural  logarithms  is  the  number  2.7183  and  is  usually 
represented  by  the  letter  e.  The  log  of  base  e  to  base  10  is  2.3026.  Base  e  is 
the  one  to  which  the  term  logarithmic  decrement  (as  used  in  the  law)  refers. 
The  base  of  common  logarithms  is  10. 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  97 

aerial,  the  amount  of  oscillating  current,  the  wave  length  and  the  distance 
of  transmission  in  a  formula,  which  will  be  found  in  appendix  A,  last 
part  of  table  7,  and  the  working  of  the  formula  illustrated  in  tables  8,  9, 
10,  11  and  12.  Eef erring  to  table  9,  it  is  found  in  practice  that,  while  the 
relative  distances  given  are  approximately  correct,  usually  the  reliable 
working  distance  is  about  two-thirds  of  that  given  in  the  table. 

Subsequent  experiments  tend  to  prove  that  the  formula  is  correct. 
Therefore,  the  tables  (while  not  absolutely  correct,  except  for  good  weather 
conditions  and  expert  operators  with  the  best  receiving  apparatus)  are 
relatively  correct  and  repay  careful  study. 

EFFICIENCY  OF  RECEIVING   APPARATUS. 

154.  Fessenden  in  his  published  account  of  his  experiments  on  the 
sensitiveness  of  wireless  telegraph  detectors  states  that  in  the  most  sen- 
sitive detectors  the  least  amount  of  work  which  will  render  a  signal 
readable  is  .007  erg  per  dot. 

If  a  dot  lasts  -zr-  of  a  second  this  represents  approximately  .01  erg 

per  second,  or  -^-r^  watts. 

Dr.  L.  W.  Austin's  tests  of  telephones  in  1908,  several  years  subsequent 
to  Fessenden's  experiment,  indicated  that  in  order  to  produce  audible 

3 
sound  in  a«telephone  not  less  than  yy—  watts  were  required.    With  tele- 
phones of  the  sensitiveness  previously  available  it  required  not  less  than 

3  . 

:j-^  watts.    With  test  telephones  of  the  sensitiveness  available  in  1914, 

Dr.  Austin  estimates  the  power  required   (at  1000  sparks  per  second) 

4 
to  make  the  electrolytic  detector  function  audibly,  as  ztt.—  watts. 

Standard  reed  telephones  in  1914,  at  600  sparks  per  second  give  an 

Q 

audible  sound  with  an  expenditure  of  the  order  of  -^rv.  watts. 

lO^'* 

INCREASE  OF  EFFICIENCY  DUE  TO  A  HIGH  SPARK  FREQUENCY. 

155.  If  two  alternating  currents  of  the  same  intensity  but  of  different 
frequencies  be  sent  through  a  telephone,  it  is  found  that  the  sound  in 
the  telephone  produced  by  the  current  of  higher  frequency  is  much 
louder  than  that  produced  by  the  lower.  This  fact  is  due  in  part  to  the 
peculiarities  of  the  human  ear,  which  is  more  sensitive  to  high-pitched 
sounds  than  to  low,  also  in  part  to  the  diaphragm  of  the  telephone,  which 
is  usually  of  such  a  weight  and  size  as  to  vibrate  most  readily  to  a  sound 
of  rather  high  pitch.  This  fact  has  an  important  bearing  on  wireless 
telegraphy,  for  the  pitch  of  the  sound  produced  in  the  telephone  con- 

7 


98  MANUAL    OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 

nected  to  the  detector  at  the  receiving  station  depends  simply  on  the 
number  of  wave  trains  per  second  at  the  sending  station.  In  order  to 
determine  exactly  what  is  the  relation  between  the  strength  of  current 
required  to  produce  an  audible  sound  in  the  telephone  and  the  frequency, 
a  series  of  experiments  was  carried  out  on  a  pair  of  head  telephones  of 
the  type  ordinarily  used  in  wireless  telegraphy,  the  results  of  which  are 
shown  in  the  table. 


'requency 

per 
second. 

Volta  to 

produce 

audible  sound. 

Frequency 

per 

second. 

Volts  to 

produce 

audible  sound, 

60 

6200  X  10-T 

540 

80  X  10-7 

120 

2900 

660 

30 

180 

1700 

780 

11 

300 

600 

900 

6 

420 

170 

In  the  first  column  are  given  the  frequencies  or  the  number  of  wave 
trains  per  second,  and,  in  the  second,  the  number  of  volts  of  alternating 
current  which  it  would  be  necessary  to  apply  to  the  terminals  of  the  tele- 
phone to  produce  an  audible  sound.  From  this  it  is  seen  that  it  requires 
about  a  thousand  times  as  much  voltage  at  a  frequency  of  60  to  produce 
a  sound  as  is  required  at  a  frequency  of  900.  We  may  assume,  therefore, 
that  if  the  number  of  wave  trains  at  the  sending  station  be  increased  from 
60  to  900  per  second,  and  the  spark  length  be  kept  the  same,  the  effect 
at  the  receiving  station  would  be  increased  one  thousand  times.  If  the 
number  of  sparks  be  increased  in  this  way  without  reducing  the  spark 
length,  it  is  evident  that  the  energy  made  use  of  at  the  sending  station 
must  be  greatly  increased.  It  will  be  more  interesting,  therefore,  to 
calculate  what  the  increase  in  sending  efficiency  of  the  station  will  be 
with  increasing  spark  frequency,  if  the  total  energy  be  kept  constant.  So 
if  we  assume  that  the  energy  is  proportional  to  the  number  of  wave  trains, 
and  divide  the  relative  increase  in  loudness  of  sound  in  the  telephone  at 
the  receiving  station,  for  any  frequency,  by  the  relative  increase  of  the 
number  of  wave  trains  per  second,  we  will  have  a  fair  comparison  of  the 
efficiencies  at  the  two  frequencies. 

Streng-th  Strength 

Frequency.  of  Frequencj'.  of 

sigrnal.  signal. 

120  1  540  13 

240  1.5  900  64 

The  results  of  such  calculations  are  seen  in  the  table,  which  shows  that 
there  would  be  very  slight  advantage  in  replacing  a  60-cycle  alternator 
giving  120  wave  trains  per  second  with  a  120-cycle  giving  240  wave 
trains,  but  that  the  advantage  increases  rapidly  as  the  frequency  is 
increased.  The  maximum  sensitiveness  of  the  telephone  appears  to  lie  in 
the  neighborhood  of  900. 


MANUAL    OF    RADIO    TELEGRAPHY   AND   TELEPHONY.  99 

156.  In  addition  to  the  increase  of  sensitiveness  of  the  telephone  at 
high  frequencies,  there  are  other  quite  independent  advantages  in  the 
use  of  a  high-pitched  spark.  First,  it  is  found  in  practice  that  a  high- 
pitched  musical  signal  is  much  more  readily  distinguished  at  the  receiving 
station  in  the  midst  of  ordinary  interference  and  atmospheric  disturb- 
ances; and  second,  at  the  sending  station  a  shorter  spark  gap,  which 
would  generally  be  used  with  a  high  frequency  spark,  puts  less  strain  on 
the  insulation  of  the  condensers  and  other  parts  of  the  circuit,  and  re- 
duces the  losses  due  to  brush  discharges,  which  in  many  stations  amount 
to  a  considerable  share  of  the  total  amount  of  power  employed. 

A  third  advantage  is  that  with  a  high  spark  frequency  larger  amounts 
of  energy  can  be  radiated  from  a  moderate-sized  aerial  without  sub- 
jecting it  to  excessively  high  potentials. 

Experiments  have  been  recently  carried  out  in  which  it  has  been  shown 
that  in  moderate  frequencies  with  stationary  spark  gaps  there  are 
nearly  always  secondary  discharges,  irregular,  but  giving  very  high  tones, 
so  that  the  real  advantage  of  the  high  spark  frequency,  from  the  stand- 
point of  telephone  sensitiveness,  is  usually  less  than  that  indicated  in 
the  table.  The  advantages  of  ease  of  reading,  the  lessening  of  the  strain 
on  the  condensers  and  insulators,  and  the  increase  in  effective  energy 
capacity  of  the  antenna,  especially  when  the  latter  is  small,  are  very 
marked,  so  that  it  has  been  found  possible  to  obtain  the  same  results  with 
small  wireless  sets  of  2  K.  W.  capacity  where  formerly  5  to  10  K.  W.  were 
employed. 

The  only  difficulty  involved  in  using  very  high  spark  frequencies  lies 
in  the  cooling  of  the  spark  gap.  For  this  purpose  a  rotary  gap  or  some 
special  refrigerating  device  must  be  used. 

For  the  reasons  stated  above,  500  cycles  has  been  adopted  as  a  standard 
frequency  for  the  alternators  of  spark  sets. 

When  receiving  from  a  sender  like  an  arc,  producing  continuous  oscil- 
lations, efficiency  is  secured  in  a  manner  which  will  be  described  under 
"  Eeceiving  Apparatus,"  chapter  VII. 

COMPARISON  OF  EFFICIENCY  USING  DAMPED  AND  UNDAMPED  WAVES. 

The  undamped  wave  is  superior  in  efficiency  to  the  damped  wave,  for 
transmitting,  due  to  some  extent  to  the  decrease  in  absorption  using  un- 
damped waves,  but  mainly  to  the  efficiency  of  the  receiving  oscillating 
audion  in  comparison  with  the  receiving  methods  used  in  reception  of 
spark  signals,  and  also  to  the  fact  that  longer  waves  are  used  in  trans- 
mitting with  damped  waves. 

LOSSES  IN  RECEIVING   CIRCUITS. 

157.  The  losses  due  to  high  frequency  resistance  in  receiving  circuits  are 
the  same  as  in  sending  circuits,  except  that  there  is  less  difference  in 


100  MANUAL    OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 

smaller  wire  between  the  direct  current  resistance  and  the  high  frequency 
resistance. 

Naval  specifications  require  that  the  decrement  of  receiving  circuits  shall 
not  exceed  .3,  while  for  sending  sets  the  limit  is  .15.  Specifying  the  high- 
est permissible  decrement  of  the  receiving  circuits  is  a  change  from  former 
practice,  which  was  that  the  d.  c.  resistance  should  not  exceed  4  ohms  per 
millihenry. 

158.  Dr.  Austin  has  shown  that  the  most  efficient  coupling  of  the 
detector  circuit  and  aerial  is  when  the  incoming  energy  is  divided  equally 
between  the  two  and  that  then  the  loudest  signals  are  produced. 

He  has  also  shown  that  the  loudness  of  the  sound  in  a  telephone  varies 
directly  with  the  power  applied,  that  is,  with  the  square  of  the  potential 
or  oscillating  current  (art.  117).  This  assumes,  of  course,  as  a  primary 
essential  of  efficiency  of  receiving  apparatus,  accurate  tuning  of  both  the 
open  and  closed  receiving  circuits  to  the  incoming  wave  length. 


Chapter  VI. 

SENDING  APPARATUS. 

GENERATORS. 

159.  Induction  coils  (fig.  14b)  with  hammer  breaks  operated  by  direct 
current  have  been  used  to  a  very  limited  extent  for  naval  purposes.  The 
vibrations  of  the  hammer  were  difficult  to  regulate  and  the  large  size 
necessary  to  handle  large  currents  made  the  frequency  too  low  for 
successful  work.  Hammer  breaks  were  soon  discarded  and  make  and 
break  regulated  by  some  form  of  rotary  motion.  The  most  successful 
form  was  the  mercury  turbine  interrupter.  This  interrupter  was  installed 
in  the  circuit  containing  the  sending  key  and  the  primary  winding 
of  the  induction  coil.  The  interrupter  consisted  of  a  direct-current 
motor  driving  a  centrifugal  pump  which  revolved  in  a  chamber  of  mercury. 
The  mercury  was  connected  to  one  side  of  a  break  in  one  leg  of  the 
primary  circuit.  It  was  drawn  up  by  the  pump  and  delivered  as  a  jet 
through  a  revolving  nozzle.  The  mercury  jet  during  a  portion  of  each 
revolution  struck  a  metallic  segment  connected  to  the  other  side  of  the 
break  in  the  circuit,  and,  if  the  sending  key  was  closed,  thereby  completed 
the  circuit  and  built  up  a  current  in  the  induction  coil  which  charged  the 
sending  condensers.  When  the  jet  passed  the  segments,  the  circuit  was 
broken.  (The  jet  passed  through  grain  alcohol  which  absorbed  the  spark 
at  break.)  This  make  and  break  occurred  once  in  each  revolution.  The 
motor  made  approximately  1800  revolutions  per  minute.  Assuming  that 
the  condenser  was  discharged  only  on  the  break,  this  gave  but  30  dis- 
charges per  second,  or  a  note  two  octaves  *  lower,  as  compared  with  120 
discharges  from  a  60-cycle  alternator.  The  operation  of  these  sets  was 
much  improved  by  increasing  the  number  of  segments  and,  therefore,  the 
number  of  makes  and  breaks  per  second,  as  many  as  six  being  used,  thus 
giving  a  spark  note  slightly  higher  than  that  of  a  60-cycle  alternator. 

The  spark  in  the  interrupter  at  break  always  carbonized  some  alcohol 
and  the  latter  also  became  mixed  with  mercury  and  formed  a  more  or  less 
conducting  carbon-mercury-alcohol  emulsion,  so  that  the  interrupter  and 
contents  required  frequent  cleaning,  washing,  and  filling. 

•  The  octave  of  a  note  is  that  differing  from  it  by  8  notes  of  the  scale 
— do-re-mi-fa-sol-la-si-do — the  octave  above  having  twice  as  many  vibrations 
per  second  and  the  octave  below  having  one-half  as  many  vibrations  as  the 
note  referred  to.  Standard  tuning  forks  vibrate  256  times  per  second.  The 
pitch  of  a  note  is  the  number  of  vibrations  per  second  producing  that  note. 


102  IfAl-TDAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 

For  small  powers  these  sets,  with  care,  gave  good  results,  and  being 
generally  used  with  mechanical  recording  apparatus  the  spark  note  was 
not  of  marked  importance. 

CONSIDERATIONS  GOVERNING  FREQUENCY  OF  GENERATORS. 

160.  Turbine  interrupters  were  practically  entirely  replaced  by  60- 
cycle  alternating  current  generators  operated  by  motors  (on  ships  and  at 
navy  yards)  or  oil  engines  (isolated  shore  stations  and  light  ships). 
These  in  turn  have  been  replaced  by  500-cycle  generators  operated  by 
motors  or  engines  as  above.  No  special  description  of  generators  will  be 
given. 

Sixty-cycle  current  was  first  selected  because  alternators  of  this  fre- 
quency were  commercial  articles.  When  the  use  of  telephones  with  receiv- 
ing sets  became  general  it  was  realized  that  a  sound  of  a  higher  note  was 
desirable  and  that  for  the  very  best  results  the  frequency  (pitch)  of  this 
note  should  be  that  to  which  the  telephone  diaphragm  or  the  operator's 
ear,  or  both,  are  most  sensitive.  A  pure  spark  note  is  produced  when 
the  spark  gap  is  so  adjusted  that  the  condenser  discharges  but  once  per 
alternation,  thus  sending  out  but  one  wave  train  per  alternation.  The  pres- 
ent standard  of  500  cycles  affords  general  satisfaction,  though  the  ears  of 
some  operators  are  more  sensitive  to  a  lower  frequency  (see  art.  155) . 

161.  To  ensure  a  perfectly  regular  condenser  discharge  and  thus  obtain 
but  one  wave  train  per  alternation,  some  generators  have  a  disk  mounted 
on  an  extension  of  the  main  shaft  and  revolving  with  it.  This  disk 
carries  projecting  electrodes,  one  for  each  pole  of  the  alternator,  equally 
spaced  like  the  spokes  of  a  wheel  and  connected  to  one  side  of  the  closed 
circuit.  (See  fig.  52.)  In  revolving  they  pass  very  close  to  a  fixed  elec- 
trode, or  spark  point,  connected  to  the  other  side  of  the  circuit,  sparking 
taking  place  as  the  points  pass — one  series  of  oscillations  for  each  alter- 
nation. Generators  carrying  rotary  spark  points  must  of  necessity  be 
placed  in  or  near  the  operating  room  and  are  to  that  extent  objectionable, 
on  account  of  the  noise  of  the  spark,  the  additional  space  required,  and 
the  noise  of  revolution  which  interferes  with  receiving.  Many  attempts 
have  been  made  to  muffle  this  type  of  spark  gap,  but  without  success. 

Motor  generators,  or  generators  driven  by  engines,  except  as  stated 
above,  are  usually  arranged  for  being  started  or  stopped  from  a  distance. 
The  controlling  apparatus  is  mounted  on  a  switchboard  which  carries 
voltmeters  and  ammeters,  one  each  for  the  supply  current  and  one  each 
for  the  generator  current.  A  frequency  meter  is  also  part  of  the  switch- 
board equipment.  This  with  the  field  rheostat  of  the  motor  enables  the 
operator  to  adjust  the  speed  of  revolution  so  as  to  give  the  required 
frequency. 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  103 

TRANSFORMERS. 

162.  A  generator  designed  for  a  certain  frequency  works  best  in  con- 
nection with  a  transformer  designed  for  the  same  frequency.  If  the 
size  of  the  condenser  to  be  used  in  the  closed  circuit  is  fixed,  and  known 
to  the  designer  of  the  transformer,  the  latter  can  be  built  so  that  the 
secondary  winding  and  condenser  form  a  circuit  whose  natural  period  is 
that  of  the  generator  frequency ;  a  few  such  transformers  have  been  sup- 
plied and  are  preferred  to  those  requiring  reactance  regulators.  Neither 
generator  nor  transformer  will  work  without  overheating  at  a  frequency 
much  greater  than  that  for  which  they  are  designed  on  account  of  the 
increase  of  heating  in  the  iron  cores  and  frames,  with  increase  of  cycles 
of  magnetization  per  second. 

An  examination  of  fig.  29  will  show  that  the  generator  armature  wind- 
ing and  the  primary  winding  of  the  transformer  form  one  circuit,  and 
the  secondary  winding  and  condenser  another.  The  reactances  of  these 
circuits  should  be  such  as  to  maintain  the  charging  E.  M.  F.  and  current 
in  phase  with  each  other. 

When  60-cycle  current  was  the  standard,  transformer  windings  were 
designed  to  give  a  potential  of  from  25,000  to  30,000  volts  in  the 
secondary  when  the  primary  was  supplied  with  110-volt  current. 

Standard  transformers  now  have  a  maximum  effective  voltage  of 
25,000  when  supplied  with  220-volt  current. 

For  small  sets  both  induction  coils  (open  core)  and  closed  core  trans- 
formers are  satisfactory;  for  large  sets  closed  core  transformers  are  pre- 
ferred. Transformers  are  fitted  with  safety  spark  gaps  set  at  the  maxi- 
mum safe  sparking  potential. 

REGULATION  OF  A.  C.  SENDING  APPARATUS. 

163.  Sending  sets  work  most  efficiently  when  the  interruptions  or 
alternations  of  current  are  in  resonance  with  the  circuit  formed  by  the 
secondary  of  the  transformer  and  the  sending  condenser. 

When  running  on  open  circuit  practically  no  work  is  being  done  by 
the  motor  or  generator  except  that  necessary  to  overcome  friction. 

When  the  primary  circuit  is  closed  by  the  sending  key,  Avith  the  spark 
gap  opened,  so  that  no  sparking  takes  place,  the  secondary  of  the  trans- 
former charges  the  condenser  during  the  first  half  of  each  alternation 
and  receives  current  from  the  condenser  during  the  second  half  of  each 
alternation. 

The  load  thrown  on  the  motor  generator  by  pressing  the  key  depends 
on  the  period  in  a  cycle  at  which  contact  is  made,  but,  generally  speaking, 
it  may  be  considered  as  instantaneous  "  full  load." 

If  the  spark  gap  is  set  so  that  the  condenser  potential  breaks  it  down, 
the  oscillations  of  the  closed  sending  circuit  practically  cut  out  the 


104  MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

secondary  of  the  transformer,  so  that  a  condition  of  instantaneous  "  no 
load  "  exists  as  soon  as  the  spark  passes.  As  soon  as  these  oscillations 
cease,  the  secondary  again  begins  to  charge  the  condenser,  and  a  condi- 
tion of  almost  instantaneous  full  load  is  established.  This  interval  is 
60  short  that  the  inertia  of  the  moving  parts  of  the  motor  generator  pre- 
vents any  change  of  speed  or  voltage,  so  that  the  instantaneous  full  load 
thrown  on  when  the  key  is  closed  is  the  one  affecting  operation. 

When  the  key  is  closed  the  momentary  current  starting  at  that  instant 
depends  only  on  the  voltage  at  that  instant  and  on  the  reactance  of  the 
primary  of  the  transformer  and  of  the  generator  armature,  since  the  re- 
sistance is  very  low. 

To  control  this  sudden  rush  of  current  an  adjustable  choke  coil,  called 
a  reactance  regulator,  may  be  placed  in  the  primary  circuit.  This  coil, 
on  account  of  its  inertia,  acts  as  a  buffer  against  sudden  changes  of  cur- 
rent, and  by  means  of  its  adjustability  enables  the  phase  relation  of  the 
E.  M.  F.  and  current  in  the  circuit  to  be  varied  and  thus  the  power 
expended  to  be  controlled. 

Since  the  reactance  regulator  controls  the  power  expended,  it  controls 
the  secondary  voltage  and  the  maximum  spark  gap  that  can  be  used. 

By  placing  the  sending  key  in  shunt  around  it  and  having  an  inductive 
resistance  in  series  with  the  key,  the  reactance  regulator  can  be  adjusted 
so  that  no  sparking  will  take  place,  but  by  closing  the  key  the  current 
added  through  the  shunt  circuit  is  sufficient  to  cause  sparking  to  take 
place.  By  means  of  this  method  the  sudden  changes  from  full  to  no 
load  are  avoided  and  the  regulation  improved,  and  since  only  a  small 
portion  of  the  total  sending  current  is  broken  at  the  sending  key,  it  is 
much  easier  to  keep  the  contacts  in  good  condition. 

A  safety  switch  is  placed  in  the  primary  lead  when  the  method  of  con- 
trol described  above  is  installed.  This  switch  should  only  be  closed  when 
sending  and  should  be  opened  at  all  other  times  when  the  motor  genera- 
tor is  running. 

A  method  of  control  tried  with  fair  results  is  to  have  the  sending  key, 
by  working  auxiliary  contacts,  weaken  the  fields  of  the  motor  and 
strengthen  the  field  of  the  alternator  by  varying  the  alternator  resistance 
just  before  the  primary  circuit  is  closed.  But  no  method  has  yet  been 
developed  that  does  not  show  some  decrease  both  in  frequency  and  voltage 
between  no  load  and  a  long  dash. 

In  arc  sets,  a  large  ballast  resistance  (fig.  29d)  is  necessary  in  the  D.  C. 
current  to  steady  the  arc.  The  alcohol  feed  and  cooling  water  supply 
must  be  regulated;  in  other  respects  the  arc  is  automatic.  Arc  sets 
are  operated  by  change  of  wave  length  only — not  by  make  and  break  of 
arc  current. 

The  charge  and  discharge  of  the  condenser  when  not  sparking  is  indi- 
cated by  a  rustling  sound,  which  signifies  danger.    This  warning  applies 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  105 

equally  to  induction  coils  and  transformers,  both  terminals  of  which  are 
dangerous  when  using  alternating  current. 

On  account  of  the  small  penetrating  effect  of  high-frequency  currents 
(art.  138),  it  is  believed  that  high  voltages  when  associated  with  fre- 
quencies of  above  100,000  per  second  are  not  dangerous  to  human  life, 
but  low  frequency,  high-voltage  currents  are  very  dangerous,  and  it  must 
be  borne  in  mind  that  a  condenser  being  charged  and  discharged  at  the 
alternator  frequency  is  very  much  more  dangerous  than  when  it  is  dis- 
charging across  the  spark  gap. 

SENDING    KEYS. 

164.  The  sending  key,  or  the  auxiliary  key  operated  by  it,  except  in  arc 
sets,  is  placed  in  one  leg  of  the  primary  circuit.  In  arc  sets  the  sending 
key  is  used  merely  to  short  circuit  part  of  the  aerial  inductance,  i.  e.,  it 
merely  changes  the  wave-length ;  the  arc  itself  is  not  broken.  This  is  neces- 
sary because  it  takes  time  to  start  an  arc. 

When  placed  directly  in  the  primary  circuit,  sending  keys,  in  some 
cases,  have  condensers  shunted  around  them  to  absorb  the  spark  at  break. 
Their  contacts  when  used  to  break  the  primary  current  direct,  are 
larger  than  in  the  ordinary  telegraph  key  on  account  of  the  larger  cur- 
rents handled.  In  other  respects  they  resemble  the  telegraph  key.  When 
used  to  operate  a  relay,  the  ordinary  telegraph  key  fills  all  requirements. 
The  relay  consists  of  a  solenoid  energized  by  the  sending  key,  its  arma- 
ture making  and  breaking  the  primary  current  in  air  or  oil. 

Figs.  37  and  39  illustrate  types  of  sending  keys.  The  Slaby  Arco 
keys  shown  in  fig.  37  were  of  massive  construction  and  very  rugged. 
Fig.  38  shows  a  solenoid  break,  the  connections  for  which  are  illustrated 
by  fig.  38a.  It  will  be  noted  that  this  is  a  positive  break  as  well  as  make. 
Fig.  39  is  practically  the  same  as  the  ordinary  telegraph  key  with  large 
contacts.  It  operates  direct  or  through  a  relay.  For  very  large  powers 
massive  solenoid  breaks  in  parallel  are  necessary,  which  require  special 
attention  in  the  design  to  permit  rapid  operation. 

Sending  keys  should  be  adjusted  to  have  just  sufficient  movement  to 
prevent  arcing  and  permit  well  defined  making  and  breaking. 

For  direct  breaking,  though  platinum  contacts  are  largely  used,  com- 
paratively large  brass  or  silver  contacts  are  satisfactory.  All  contacts 
must  be  kept  smooth  and  clean  and  their  faces  parallel. 

What  is  known  as  a  "  break  key  "  is  preferred.  It  was  first  used  on 
the  Stone  sets,  and  is  an  ingenious  and  useful  device  for  "listening  in" 
while  sending.  An  attachment  to  the  sending  key  breaks  the  detector 
circuit  just  before  the  sending  key  makes  contact.  When  the  sending 
key  is  released  the  receiving  circuit  is  automatically  cut  in,  so  that  the 
receiver  can  "  break  "  the  sender  by  a  call,  which  the  latter  can  hear  in 
the  interval  between  his  letters  or  words. 


106  MAJSrUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


r^         ^ 


T' 


£^ 


FiQ.  37.— Slaby  Arco  Key. 


Fig.  38. 


r»/A(^RAM   or  CONNECTIONS 


mj] 


(^0 


-■        ^^ 


TRANSrORMER 
PI?|MARr 


ma 


TO  no  VOLTS  D.C. 

► 


Fig,  38a.— Solenoid  Key. 


Fig.  39.— Wireless  Specialty  Apparatus  Co. 


MANUAL    OF    KADIO    TELEGRAPHY    AND   TELEPHONY.  107 

For  sending  time  signals,  a  Western  Union  relay  closes  a  local  battery 
having  in  circuit  a  solenoid,  whose  armature  carries  a  lever  which  presses 
and  releases  the  sending  key  in  unison  with  the  current  impulses  sent 
from  the  standard  clock  at  the  Naval  Observatory  in  Washington. 

CLOSED  CIRCUITS   (INDUCTANCE,  CONDENSER,  SPARK  GAP)  . 

165.  Sending  circuits  are  illustrated  by  elementary  diagrams  in  figs. 
29  to  29e  and  40  to  48  inclusive.  The  symbol  |  indicates  alternating 
current.  The  names  under  figures  are  those  of  the  engineers  proposing 
or  designing  sets  with  the  connections  shown. 

To  render  them  capable  of  adjustment  all  wireless  telegraph  oscillat- 
ing circuits  have  either  variable  inductances  or  condensers  or  both. 
These  condensers  and  inductances  vary  greatly  in  design.  Those  for 
sending  circuits,  especially  on  account  of  the  high  potentials  to  which  they 
are  subjected,  are  very  different  in  construction  and  mounting  from  those 
used  in  receiving  circuits. 

Fixed  condensers  and  variable  inductances  are  used  in  sending  cir- 
cuits. The  condensers  may  be  single,  two  or  more  in  series,  or  in  parallel. 
Series-parallel  installations  may  be  made  also,  just  as  in  primary  bat- 
teries.    (See  figs.  28c  and  28d.) 

The  variable  inductance  usually  consists  of  a  helix  or  spiral  of  compara- 
tively large  bare  wire  (round  or  flat)  mounted  on  an  insulating  frame  a 
foot  or  more  in  diameter,  the  turns  of  wire  varying  from  about  |"  to  2" 
apart.     (See  figs.  72  and  73.) 

Previous  to  the  introduction  of  quenched  gaps,  the  greater  number 
of  sending  circuits  were  direct  connected,  but  inductively  connected 
sets  are  equally  efficient  and  have  this  advantage,  that  the  coupling  can 
be  readily  adjusted  independently  of  the  natural  wave  length  of  eitlier 
circuit.     (Figs.  42,  43,  and  45.) 

166.  In  direct  connected  sets,  three  movable  clips  or  sliders  are  usually 
provided,  one  for  the  closed  and  two  for  the  open  circuit  (fig.  40).  The 
closed  circuit  is  permanently  connected  to  one  end  of  the  helix  and  the 
circuit  completed  by  means  of  the  wire  from  the  movable  clip,  which  can 
be  connected  to  any  desired  point. 

The  open  circuit  has  the  ground  and  the  aerial  wire,  respectively, 
attached  to  the  other  two  clips  and  these  are  attached  to  such  points  of 
tlie  helix  as  will  give  the  open  circuit  the  same  natural  period  as  the 
closed  circuit  and  at  the  same  time  give  the  two  circuits  the  number  of 
turns  in  common  necessary  for  the  desired  coupling. 

167.  In  inductively  connected  sets,  the  closed  circuit  helix  or  spiral  is 
the  same  as  before,  the  open  circuit  helix  is  permanently  attached  to  the 
ground  lead  and  the  aerial  lead  attached  to  whatever  point  is  necessary. 
The  mutual  induction  and  coupling  are  varied  by  moving  the  open  circuit 
helix  as  a  whole.  (Figs.  42  and  43.)  Inductive  connections  are  re- 
quired with  naval  spark  sets. 


108 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


TO  AERIAL 


XO  AERIAL    k 


s 


X 
X 


DEFOREIST 
SHOEMAKEf^ 

FIG.   40 


TO  AERIAL 


TESSENDEN 
FIG.  41       -TO AERIAL 


stone: 

FIG.  42 

TO  AERfAL  , 


MARCONI 
STONC 

FIG.   43 


TO  AEf?iAL    ], 


sT 


massie: 

FIG.  44  . 


LOWENSTEIN 

FIG.   47 


TO  AERiAu 


s 


PIERCE 
SLABY  ARCO 

FIG    48 


Note. — Figures  40,  41,  42,  44,  and  48  represent  circuits  that  are  not  in 
general  use  to-day,  and  hence  to  the  student  have  a  historical  rather  than  a 
practical  value. 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY.  109 

Making  the  adjustments  to  particular  wave  lengths  and  couplings  is 
called  tuning  and  is  discussed  in  Chapter  VIII. 

168.  In  some  Telefunken  sets  (fig.  46)  the  sending  inductance  in 
both  closed  and  open  circuits  consists  of  flat  spirally  wound  coils,  mounted 
parallel  and  close  to  each  other  in  a  frame.  Alternate  coils  are  con- 
nected to  a  lever  by  which  their  position  relative  to  the  others  can  be 
varied.  The  coils  are  connected  so  that  currents  in  adjacent  coils  oppose 
each  other  and  decrease  the  self  induction  of  the  whole,  called  by  the 
manufacturers  a  variometer.  By  means  of  the  lever  the  coils  can  be 
separated  and  the  self-induction  and  consequently  the  period  of  the  cir- 
cuit regulated.  This  is  illustrated  in  fig.  46  by  an  arrow  drawn 
diagonally  across  the  inductances  in  which  it  is  used.  Fig.  74  shows  the 
apparatus  as  manufactured.  Open  spiral  inductances  are  preferable 
(Fig.  72). 

169.  For  older  direct  connected  sets  connections  shown  in  figs.  40  and 
44  were  preferred.  In  the  figures  referred  to,  the  condenser  is  directly 
across  the  secondary  terminals  of  the  transformer,  and  the  spark  gap  in 
one  leg  of  the  closed  oscillating  circuit,  as  contrasted  with  the  spark  gap 
being  placed  directly  across  the  transformer  terminals.  (Fig.  48.)  The 
former  is  considered  to  be  a  more  symmetrical  arrangement. 

Attention  is  invited  to  fig.  41,  which  shows  one  leg  of  the  trans- 
former directly  grounded  and  the  other  leg  connected  direct  to  the  aerial. 
All  other  methods  of  connection  afford  direct  path  to  ground  and  path 
through  condenser  and  spark  gap.  This  method  of  installation  affords 
path  to  ground  through  condenser  or  spark  gap  only  and  affects  tuning. 
If  the  aerial  is  touched  when  current  is  on  the  transformer,  the  latter, 
having  one  leg  grounded,  is  short-circuited  through  the  body  and  a  severe 
shock  may  be  experienced. 

Though  this  method  of  connection  is  no  longer  used,  it  is  referred  to 
here  to  show  the  necessity  of  giving  careful  consideration  to  the  relative 
positions  of  ground,  spark  gap,  and  condenser.  Errors  in  connections 
of  direct  connected  sets  are  sometimes  made  so  that  the  most  direct  path 
to  ground  is  through  tha  spark  gap.  This  induces  potentials  at  the 
gap  or  condenser  approximately  equal  to  those  at  the  upper  end  of  the 
aerial  and  produces  disagreeable  inductive  effects  in  the  operating  room. 
Some  installers  prefer  to  ground  one  leg  of  the  secondary  of  the  trans- 
former when  the  closed  circuit  is  inductively  connected,  but  this  is  con- 
sidered unnecessary. 

170.  Fig.  43  shows  the  preferred  form  of  inductive  connection  or  coup- 
ling of  a  helix,  that  is,  one  inductance  above  the  other.  This  takes  up  less 
floor  space  and  the  coupling  is  varied  by  vertical  instead  of  horizontal 
movement,  as  is  necessary  when  the  coils  are  side  by  side  as  illustrated  in 
fig.  42. 


110  MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 

Spiral  inductances  (fig.  72)  can  be  arranged  in  a  small  space  above 
one  another,  side  by  side  or  at  an  angle,  and  are  very  convenient;  they 
are  preferred  by  some  manufacturers. 

Inductances  added  to  the  aerial,  such  as  those  on  the  right  of  fig.  45, 
are  added  for  the  purpose  of  lengthening  its  period.  They  are  called 
"  loading  coils." 

Fig.  47  indicates  a  method  of  connecting  up  sending  sets  so  that  the 
operator  by  moving  a  hand  wheel  or  lever  can  change  the  wave  length  of 
the  open  and  closed  circuits  the  same  amount  without  changing  the 
coupling.  This  apparatus  is  just  being  introduced  and  should  greatly 
facilitate  the  operator's  control  over  his  sending  wave  length.  It  is  called 
a  tune  shifter. 

CONDENSERS. 

171.  For  transmitters  up  to  5  K.  W.,  standard  coppered  jars  in 
air  or  oil  are  preferred.  Tinfoil  covered  jars  are  no  longer  supplied.  The 
standard  jar  has  a  capacity  of  .002  mf.  Condenser  racks  or  tanks  are 
arranged  to  hold  a  number  of  jars  somewhat  greater  than  that  necessary 
for  the  rated  output  (see  Table  2,  Appendix  A). 

Inside  connections  to  Leyden  jars  are  best  made  by  soldering  one  end 
of  a  strip  of  copper  or  brass  gauze  to  the  inner  copper  coating  and  clamp- 
ing the  other  end  to  the  charging  bus  bar. 

Outside  connections  are  made  either  by  supporting  all  jars  on  a  con- 
ducting plate  connected  to  the  other  charging  bus  bar  or  connecting  this 
bar  to  a  strap  of  sheet  brass  or  copper  clamped  around  the  jar. 

The  important  point  about  condenser  connections  is  that  they  should 
make  a  good  electrical  contact,  of  comparatively  large  area,  with  the 
charging  wire  or  bus  bars  and  with  the  condenser  jars  or  plates.  A 
symmetrical  arrangement  of  material  giving  as  nearly  as  possible  equal 
lengths  of  discharge  paths  should  be  made. 

Many  kinds  of  springs  and  clips  for  condenser  connections  have  been 
devised  and  are  in  use,  but  none  are  better  than  those  just  described. 
Less  difficulty  is  experienced  with  connections  on  copper  coated  jars  or 
plates  than  was  the  case  when  tinfoil  was  used  exclusively  for  distributing 
the  charge  over  the  glass  dielectric. 

172.  The  condensers  now  in  use  are  standard  Leyden  jars  in  air  or 
oil.  (Fig.  49.)  CZa^s  p/a/es  in  air  or  oil  (glass  dielectric) .  Metal  plates 
in  compressed  air  (air  dielectric)  (fig.  50)  and  tinfoil  (paper  dielectric). 
For  large  powers,  glass  plates  in  oil  or  metal  plates  in  compressed  air  are 
preferred.  For  small  sets  the  most  convenient  for  use,  installation,  and 
inspection,  are  the  standard  jars,  in  air  or  oil,  or  glass  plates  set  ver- 
tically in  oil.  Fig.  49a  is  a  special  form  of  Leyden  jar  which  is  con- 
venient for  some  purposes.  The  low  voltages  associated  with  500  cycle 
sending  sets  have  made  practicable  the  use  of  paper  condensers  as  noted 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY.  Ill 


Fig.  49b. — Mica  Condenser — Dubilier 
Type. 


Fio.  49. — Leyden  Jar  Battery. 


UJ 


Fig.  49a. — Moscicki  Tube.  Fig.  50. — Compressed  Air  Condenser. 


112  MANUAL    OF   RADIO    TELEGRAPHY    AND   TELEPHONY. 

above  for  small  powers,  but  they  are  relatively  inefficient  as  compared  with 
others  mentioned. 

In  some  of  the  largest  stations,  galvanized  iron  plates  have  been 
hung  up  side  by  side  under  cover,  forming  huge  condensers,  which  require 
very  little  attention. 

173.  Practically  all  other  insulators  have  a  greater  specific  inductive 
capacity  than  air  at  ordinary  pressure,  and  nearly  all  of  them  have  a 
greater  dielectric  strength  than  air  (Table  la,  Appendix  A).  The  Leyden 
jar,  having  long  been  used  as  a  high-potential  condenser,  its  method  of 
manufacture  being  well  known,  and  the  best  glass  having  not  les  than  nine 
times  the  capacity  of  air,  has  been  very  generally  used  in  wireless  telegraph 
sending  circuits.  Air  and  oil,  while  requiring  much  larger  volume  to  give 
the  same  capacity  as  glass,  have  the  excellent  property  of  mending  them- 
selves after  puncture  by  a  spark,  while  all  kinds  of  solid  or  semisolid  die- 
lectrics require  renewal  after  rupture. 

Mica  has  very  great  dielectric  strength,  as  much  as  5000  volts  per  mil, 
and  has  been  used  to  some  extent  in  condensers  in  the  form  of  micanite. 

The  semisolid  dielectrics,  such  as  beeswax  and  paraffin,  have  to  be 
made  up  with  considerable  attention  to  the  temperatures  in  which  they 
are  to  be  used,  since  they  may  melt  in  summer  and  crack  in  winter,  but 
they  are  cheap  and  easily  obtained. 

Dielectric  strength  of  insulators  per  millimeter  increases  with  decrease 
of  thickness,  except  in  oils,  where  it  seems  to  decrease. 

Dielectric  strength  of  air  increases  with  increase  of  pressure. 

Dielectric  strength  of  air  decreases  with  decrease  of  pressure  until  the 
pressure  is  in  the  neighborhood  of  1  millimeter  of  mercury,  when  it 
increases. 

Dielectric  strength  of  a  vacuum  should  be  infinitely  great. 

Fleming  states  that  with  the  best  flint  glass  it  is  possible  to  store  about 
45  foot-pounds  of  energy  per  cubic  foot  of  glass.  The  limit  is  set  by  the 
dielectric  strength  of  glass.  He  has  shown  that  the  lengths  of  discharge 
paths  of  all  condenser  elements  should  be  equal. 

Capacity  varies  inversely  and  dielectric  strength  directly,  as  the  thick- 
ness of  the  dielectric,  but  they  do  not  vary  in  the  same  ratio. 

The  dielectric  strength  of  glass  condensers  decreases,  that  of  oil  con- 
densers increases,  with  the  frequency. 

A  table  showing  the  specific  inductive  capacity  of  a  number  of  dielec- 
trics and  their  dielectric  strengths  is  given  in  appendix  A.  This  table,  la. 
is  by  no  means  complete.  Data  relative  to  the  hysteresis  losses  of  various 
dielectrics  is  almost  lacking,  and  want  of  agreement  is  noted  among 
different  authorities. 

DIELECTRIC  STRENGTH  OF  AIR. 

174.  The  dielectric  strength  of  air  is  considered  to  be  about  4500 
volts  per  millimeter  for  gaps  of  about  1  millimeter  in  length,  and  about 
3000  volts  per  millimeter  for  gaps  of  the  length  of  a  centimeter  or  more. 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


113 


' 

—1 

' 

-1 

■^ 

/| 

"^A 

r 

<r^ 

>N 

5 

w 

?l 

K 

IN 

G 

; 

I 

31 

s 

L 

M 

4C 

.E 

•- 

I 

i? 

TV 

^^ 

Er 

1  < 

>H 

^Fi 

,P 

N 

EE 

D 

_E 

F^ 

Ol 

MTl 

S 

fJT 

vi»L- 

M 

lTC 

n 

J? 

r 

?'^ 

Ci] 

1 

ir 

101 

4  r 

d.A 

n 

tw 

rn 

m 

m 

R 

Jl 

ft 

Wf 

im 

( { 

m. 

E 

/ 

Hi 

T 

r 

/ 

y 

/ 

/ 

/ 

/ 

IS 

7 

/ 

l/ 

/ 

/ 

/ 

y 

/ 

/ 

n 

/ 

o 

/^ 

^ 

^ 

/ 

/ 

2 

•^ 

x" 

^ 

,^ 

/ 

/ 

a 

r 

•^ 

y 

r' 

/ 

/ 

S 

J 

^ 

^ 

/ 

/ 

^ 

'2 

e 

.-r* 

1^ 

h^ 

/ 

/ 

,/ 

/ 

f 

US' 

,/ 

r 

,/ 

r 

fl 

f) 

> 

.^ 

/ 

in 

2 

rt 

} 

o 

/ 

/ 

4 

y 

K 

I.C 

vc 

iiT 

e; 

/ 

/ 

19 

/' 

/ 

/ 

/ 

1 

/ 

/ 

/ 

/ 

Q 

y 

r 

/ 

y 

/ 

/ 

7 

u 

/ 

/ 

^, 

/* 

C 

/ 

/ 

6 

r 

/ 

7 

r 

/ 

y 

/ 

$■ 

/ 

/ 

/ 

A 

/' 

4 

f 

/ 

/ 

;^ 

3 

y 

/ 

i 

/ 

y 

Z 

/ 

/ 

/. 

y 

I 

• 

^^ 

^ 

t^ 

>^ 

K 

1  r 

,.0 

IT 

s 

^ 

^ 

2_ 

a_ 

--i 

a_ 

Jk 

ft- 

5^ 

-£ 

e- 

_^ 

a_ 

-^ 

L. 

f 

0  J 

ft 

?_ 

Jl 

0 

^ 

O- 

-a 

a- 

n. 

f— 

M 

£_ 

M 

B- 

FiQ.  51. 


114  MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

Fig.  51  shows  sparking  distances  for  various  voltages  in  air  between 
needle  points,  as  determined  by  experiment.  These  distances  are  usually 
greater  than  those  obtained  from  equal  voltage  between  the  blunt  spark 
points  used  in  wireless  telegraphy.  The  latter  probably  correspond  more 
closely  to  table  1,  appendix  A.  On  the  other  hand,  this  table  of  spark  dis- 
tances was  determined  by  raising  the  voltage  very  gradually  and  exactly 
alike  for  each  gap,  while  in  oscillating  circuits  there  is  a  convulsive  rush 
which  may  produce  very  high  potentials.  This  has  been  shown  by  intro- 
ducing a  minute  spark  gap  elsewhere  in  the  circuit,  the  effect  being  to 
greatly  increase  the  gap,  which  can  be  ruptured  by  a  given  transformer 
potential.  The  inertia  of  the  charge  carries  it  forward,  and  just  as  the 
inertia  of  water  in  a  pipe  produces  a  great  pressure  if  its  flow  is  suddenly 
checked,  so  the  potentials  in  the  sending  circuits  may,  and  usually  do,  rise 
much  higher  than  is  indicated  by  the  transformer  ratio. 

SPARK  GAPS. 

175.  A  great  deal  of  thought  and  ingenuity  has  been  expended  on 
improving  the  action  of  spark  gaps.  For  instance,  the  use  of  magnetic 
blowouts,  induced  and  forced  air  drafts  across  the  gap;  dividing  them 
into  a  series  of  short  gaps;  placing  gaps  in  parallel;  enclosing  them  in 
compressed  air  and  in  nitrogen  gas;  making  the  points  hollow  and  cool- 
ing them  with  air  or  water. 

Until  recently,  no  method  of  construction  for  small  powers  was  mark- 
edly better  than  the  ordinary  gap  in  air  between  two  zinc  rods,  i  to  i^ 
inch  in  diameter.  There  are  two  points  in  common  for  all  good  working 
gaps — (a)  The  sparking  surfaces  must  be  clean  and  fairly  smooth;  (b) 
They  must  be  kept  from  heating. 

The  increased  radiation  from  cooled  spark  electrodes  as  compared  with 
heated  ones  is  very  evident. 

Heated  surfaces  give  off  more  metallic  vapor  and  tend  to  the  forma- 
tion of  a  low  frequency  arc. 

There  is  no  doubt  that  much  of  the  irregularity  noted  in  sending  is  due 
to  an  improperly  adjusted  spark  gap  and  the  effect  known  as  "  soaring  " 
or  "  swinging  "  is  probably  due  to  the  inequalities  in  the  action  of  the 
spark  gap  and  condensers  caused  by  heat. 

An  open  spark  must  be  kept  white  and  crackling  and  have  considerable 
volume.    If  too  long,  it  will  be  stringy ;  if  too  short,  an  arc  will  be  formed. 

All  spark  gaps  are  adjustable — either  in  length  or  in  number.  All 
should  be  well  muffled  for  obvious  reasons. 

The  types  of  spark  gaps  now  in  use  are  shown  in  figs.  52-57.  The 
only  types  now  supplied  are  fig.  52,  the  synchronous  rotating  gap,  and 
fig.  57,  quenched  gap.  Fig.  57  illustrates  only  one  form  of  the  quenched 
gap.  It  is  made  in  other  equally  efficient  forms  following  the  same 
principle;  viz.,  a  series  of  very  short  gaps  (arts.  85  and  180). 


MANUAL   OF    EADIO    TELEGRArHY    AND   TELEPHONY. 


115 


SPARK     GAPS 


SHArx   or 
ALTERNATOF^ 


5     t 


SYNCHRONOUS    ROTATING  SPARK  GJ\P  NON-SYNCHRONOUS  ROTATING;  SPARK  QAP 


FIG     52 


FiG.    53 


AIR   '^f^ 


FIG     54 


FIG.   55 


u 


AIR  BLAST     QAP 


PARALLEL   qAP 


<€ 


4 


M( 


A 


w 


f1\ 


"^ 


rh 


VU 


m 


w 


m 


CI 


03 


a 


QyeNCHCD    SPARK    aAP 
FIG.    57 


=^^=l=D^ 


(0   (0 


MARCONI    DISC    DISCHARGER 
FIG.   56 


FIG.   58       T-ELEFUINIKEN 
(Now   Obsolete) 


FIG.   59       STONEl 
(Now   Obsolete) 


MASSIE    QAP    FOR    COMPRESSED  AlR  FESSENDEN-J)E  FOREST 


FIG.  60 
(Now  Obsolete) 


FIG.   61 
(Now  Obsolete) 


116  MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

176.  The  function  of  the  spark  gap  in  an  oscillatory  circuit  is  to  allow 
the  condenser  to  charge  to  the  required  potential,  and  then  to  break  down 
and  permit  the  charge  to  surge  back  and  forth  until  its  energy  is  dis- 
sipated. The  ideal  spark  gap  would  be  one  which  would  insulate  per- 
fectly while  the  condenser  was  charging  and  conduct  perfectly  while  it 
was  discharging,  and  the  nearer  these  conditions  can  be  fulfilled  the  more 
efficiently  will  the  spark  gap  perform  its  duty.  Either  condition  can  be 
fulfilled  alone,  but  the  combination  is  somewhat  difficult  to  obtain. 

The  resistance  of  the  spark  gap  when  the  discharge  is  passing  depends 
upon  two  factors;  it  increases  rapidly  with  the  spark  length,  and  de- 
creases rapidly  with  the  oscillatory  current,  amounting  with  a  half-inch 
gap  to  several  hundred  ohms  when  a  fraction  of  an  ampere  passes,  and  a 
small  fraction  of  an  ohm  when  50  or  60  amperes  are  flowing.  With  the 
spark  length  above  half  an  inch,  the  resistance  with  the  same  oscillatory 
current  flowing  may  be  taken  as  roughly  proportional  to  the  spark 
length.  But  in  a  condenser  circuit  the  amount  of  electricity  stored  up  in 
the  condenser,  and  hence  the  amount  of  oscillatory  current,  increases 
with  the  spark  length.  Thus  we  have  two  conditions  working  against 
each  other  as  regards  the  influence  of  the  spark  length  on  the  spark 
resistance;  but  we  can  increase  the  amount  of  current  flowing  without 
increasing  the  spark  length  by  increasing  the  size  of  the  condenser,  and 
the  most  efficient  form  of  circuit  for  a  given  power  is  that  in  which  a 
moderate  spark  length  and  large  condensers  are  used. 

When,  after  the  condenser  is  charged,  the  spark  gap  breaks  down,  the 
gap  becomes  filled  with  metallic  vapor  and  for  the  time  being  forms  a 
high-frequency  alternating  current  arc.  It  is  the  presence  of  the  metallic 
vapor  which  produces  the  conductivity  of  the  spark.  After  the  discharge 
ceases,  however,  if  this  metallic  vapor  is  not  removed  from  the  gap,  the 
insulation  will  evidently  be  poor  at  the  time  that  the  condenser  is  next 
being  charged,  hence  the  first  condition  of  spark  efficiency  would  be  want- 
ing. It  is  therefore  necessary  to  remove  this  vapor  completely  as  soon  as 
possible  after  the  surgings  of  the  condenser  charge  cease.  This  is  done 
partly  by  cooling  the  electrodes  of  the  spark  gap,  thus  stopping  the 
vaporization,  and  in  some  cases  by  blowing  the  vapors  out  of  the  gap. 

177.  In  the  simple  gap,  such  as  is  found  in  sets  of  small  power,  the 
vapor  is  usually  sufficiently  dissipated  by  the  natural  cooling  of  the 
electrodes  and  by  ordinary  air  currents.  Such  a  gap,  however,  not  pro- 
vided with  an  air  blast,  should  not  be  enclosed.  For  somewhat  larger 
powers,  an  air  blast  is  ordinarily  considered  necessary.  This  carries 
away  the  metallic  vapors  and  at  the  same  time  cools  the  electrodes.  Such 
an  arrangement  is  shown  in  fig.  54. 

Another  form  of  gap  for  small  powers  which  gives  good  satisfaction 
is  the  parallel  gap  (see  fig.  55),  in  which  two  cylinders  of  zinc  or  brass 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  117 

are  placed  parallel  to  each  other,  and  the  spark  runs  from  point  to  point, 
never  jumping  twice  consecutively  in  the  same  place.  This  wandering 
of  the  spark  is  facilitated  by  a  slight  roughening  of  the  electrodes  with 
a  file.  The  explanation  of  this  phenomenon  of  the  running  spark  is 
probably  as  follows:  The  spark  jumps  from  a  slight  projection  on  the 
electrode  which  in  the  course  of  the  oscillations  is  burned  away,  so  that 
at  the  next  discharge  an  easier  path  is  found  from  some  other  projecting 
point. 

178.  For  high  powers,  a  good  form  of  spark  gap  is  the  rotating  5301- 
chronous  gap  shown  in  fig.  52,  This  consists  of  one  or  more  stationary 
members  and  a  rotating  member  made  up  like  a  wheel  with  projecting 
spokes.  This,  in  its  best  form,  is  attached  directly  to  the  shaft  of  the 
alternator,  and  is  so  adjusted  that  a  spoke  comes  opposite  a  stationary 
member  at  the  exact  moment  that  the  maximum  of  potential  is  obtained 
in  the  condenser.  This  insures  one  discharge  for  each  alternation  of  the 
current,  the  complete  absence  of  conducting  vapors,  and  gives  a  satisfac- 
tory insulation  for  each  spark.  The  regularity  of  discharge  from  this 
form  of  gap  produces  a  pure  musical  note,  which  is  of  great  importance 
in  the  telephonic  reception  of  signals.    (See  art.  156.) 

179.  Another  form  of  rotating  gap,  called  the  non-synchronous  rotat- 
ing gap,  is  shown  in  fig.  53.  In  this  the  wheel  is  rotated  rapidly  by  an 
independent  motor  without  regard  to  synchronism  with  the  alternator. 
The  face  of  the  stationary  member  of  the  gap  forms  an  arc  of  a  circle 
long  enough  to  a  little  more  than  cover  the  distance  between  two  spokes, 
thus  alwa3's  insuring  the  proper  sparking  distance.  The  rotating  wheel 
itself  forms  an  efficient  fan. 

180.  What  is  called  a  "  quenched  gap  "  (fig.  57)  may  be  made  up  of  a 
number  of  copper  discs  accurately  turned  and  separated  by  annular  rings 
of  mica  about  .01  inch  thick.  The  spark  is  confined  to  the  air  tight 
space  inside  the  mica-rings.  It  has  almost  entirely  displaced  open  gaps 
(art.  175). 

This  type  of  gap,  if  a  proper  number  of  discs  are  in  series,  also  gives 
one  discharge  for  each  alternation  of  the  current  and  produces  the  same 
pure  musical  note  as  the  synchronous  gap. 

It  is  almost  noiseless  and  has  the  further  advantage  of  (probably  on 
account  of  its  large  cooling  surface)  quickly  stopping  the  oscillations  of 
the  closed  circuit,  so  that  the  open  circuit  is  left  free  to  vibrate  in  its  own 
period,  and  it  therefore  radiates  waves  of  but  one  length.  This  fact  haa 
an  important  bearing  on  the  tuning  of  wireless  telegraph  sets  and  also  on 
the  coupling,  which  can  without  change  of  wave  length  be  made  that 
which  will  transfer  energy  from  the  closed  circuit  to  the  open  circuit 
with  the  least  loss  (art.  85) . 


118  MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

The  quenched  gap  can  not  be  depended  upon  to  operate  without 
artificial  cooling  of  the  discs  when  any  but  very  small  powers  are  used. 
Like  all  other  gaps,  its  action  is  improved  by  an  air  blast. 

181.  In  the  case  of  the  rotating  gap  the  equivalent  air  velocity  in  a  case 
of  large  power  was  about  20,000  feet  per  minute.  Mr.  J.  Martin  finds  a 
very  distinct  gain  in  radiation  from  an  air  cooled  gap  with  air  pressures 
up  to  15  pounds  per  square  inch,  which  corresponds  to  a  velocity  of 
82,000  feet  per  minute,  or  about  1400  feet  per  second. 

Take  a  single  gap  operating  on  a  1000-meter  wave  on  the  peak  of  the 
charging  E.  M.  F. :  If  the  coupling  between  the  open  and  closed  circuits 
is  such  that  the  closed  circuit  transfers  all  its  energy  to  the  open  circuit 
in  five  complete  vibrations  the  first  group  of  sparks  will  last  1/30,000 
second.  To  remove  the  conducting  vapor  from  the  gap  in  that  time  would 
require  a  minimum  air  velocity  across  the  gap  of  1000  feet  per  second  if 
the  electrodes  were  .4  inch  (1  cm.)  in  diameter.  From  this  point  of  view 
it  would  seem,  therefore,  that  any  gap  will  act  as  a  quenched  gap  if  the 
air  velocity  across  the  gap  is  sufficiently  great,  and  that  the  required  air 
velocity  varies  directly  as  the  diameter  of  the  spark  electrodes — inversely 
as  the  wave  length,  directly  as  the  damping — and  (since  it  is  known  that 
close  coupling  increases  the  damping)  directly  as  the  percentage  of 
coupling. 

Loose  coupled  circuits  would  require  a  lower  air  velocity  than  close 
coupled  ones. 

Fig.  56  illustrates  the  Marconi  disc  discharger,  which  is  practically 
the  same  in  principle  as  fig.  53 — the  non-synchronous  rotating  gap.  A 
special  motor  is  required  to  operate  the  discharger.  It  has  also  the  dis- 
advantage of  being  as  noisy  as  the  synchronous  gap.  The  disc  discharger, 
like  the  synchronous  rotating  gap,  is  suitable  for  large  powers  and  for  use 
with  direct  as  well  as  alternating  current.  It  is  fitted  with  an  auxiliary 
stationary  gap  for  use  in  case- of  motor  breakdown. 

USE  OF  THE  ARC  FOR  PRODUCING  UNDAMPED  OSCILLATIONS. 

182.  The  arc  method  of  producing  undamped  oscillations  with  direct 
current  was  discovered  by  Professor  Elihu  Thompson  in  1892  and  has 
been  developed  by  many  other  investigators.  In  order  to  prevent  the 
oscillations  from  running  back  to  the  dynamo,  choke  coils  or  very  high 
resistances  must  be  placed  in  the  D.  C.  leads. 

When  the  shunt  containing  inductance  and  capacity  is  closed  around 
the  arc  in  a  circuit  like  that  shown  in  fig.  29d,  62  or  91,  a  part  of  the  cur- 
rent fiows  into  the  condenser,  thus  robbing  the  arc  of  a  part  of  its  current ; 
but  as  the  D.  C.  potential  across  an  arc  increases  as  the  current  decreases, 
this  decrease  in  current  increases  the  potential  difference,  and  the  con- 
denser continues  to  charge.    At  the  next  instant,  however,  the  condenser 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


119 


commences  to  discharge,  increasing  the  direct  arc  current  until  it  is 
entirely  discharged ;  then  the  process  repeats  itself. 

Oscillations  can  be  produced  in  this  way  from  almost  any  form  of  arc 
and  over  a  wide  range  of  voltages,  but  it  is  found  that  high  frequency 
oscillations  are  best  produced  when  the  direct  current  voltage  is  high 
(500  volts  or  more),  and  when  the  positive  arc  electrode  is  capable  of 
conducting  away  heat  rapidly.  Water  is  used  as  a  cooling  medium  instead 
of  air,  as  with  a  spark  transmitter,  and  to  facilitate  its  application,  the 
positive  (copper)  electrode  is  made  hollow.  This  rapid  cooling  of  the  arc 
plays  a  very  important  part  in  the  production  of  the  oscillations,  as  it 
causes  the  arc  to  die  down  rapidly  and  increases  the  suddenness  with  which 
the  current  flows  into  the  condenser.  It  has  also  been  found  that  when  the 


PILOT  LAMP 


Fig.  62. — Arc  Arranged  for  Wireless  Telephony. 


arc  is  formed  in  an  atmosphere  capable  of  assisting  in  this  cooling,  the 
energy  of  the  oscillations  is  vastly  increased.  The  best  gaseous  conductor 
of  heat  is  hydrogen,  and  consequently  the  best  results  are  obtained  in  an 
atmosphere  of  hydrogen  or  some  mixed  gas  or  vapor  containing  hydrogen. 
Common  illuminating  gas  gives  excellent  results,  and  recently  alcohol 
and  ether  introduced  into  the  arc  chamber  drop  by  drop  and  vaporized 
by  the  heat  of  the  arc  has  come  into  use.  It  has  been  suspected  that  these 
gases  and  vapors  may  have  some  effect  on  the  electrical  conductivity  of 
the  arc  as  well  as  on  its  cooling,  but  this  point  is  still  unsettled. 

The  energy  of  the  oscillations  which  can  be  obtained  from  the  arc  is 
mcreased  by  forming  it  in  a  magnetic  field  the  lines  of  force  of  which  are  at 
right  angles  to  the  arc  length.  The  action  of  the  magnetic  field  is  twofold ; 
first  it  deflects  the  arc  to  one  side,  increasing  its  length  and  consequently 
the  difference  of  potential  between  the  arc  electrodes,  and  second,  it  blowa 
out  of  the  field  the  conducting  ions  formed  in  the  gas,  thus  decreasing 
the  arc  conductivity  and  still  further  increasing  the  difference  of  potential 
between  the  electrodes  (fig.  29e,  art.  94). 


120  MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

For  the  successful  production  of  oscillations  a  correct  relation  must 
exist  between  the  arc  current,  the  arc  length,  and  the  strength  of  the 
magnetic  field.  This  relation  in  general  can  be  obtained  only  by  ei- 
periment.  If  these  adjustments  are  not  correctly  made  several  sets  of 
useless  superposed  oscillations  may  be  produced  in  the  condenser  circuit 
Therefore  it  is  necessary  in  working  with  waves  produced  from  the  arc 
to  examine  its  oscillations  from  time  to  time  with  the  wave  meter,  in 
which,  if  the  adjustment  be  correct,  but  one  sharp  and  powerful  maxi- 
mum will  be  found. 

THE  FEDERAL-POULSEN  SYSTEM  OF  RADIO  TELEGRAPHY. 

This  system  uses,  for  radio  transmission,  an  undamped  or  continuous 
electromagnetic  wave,  as  distinguished  from  the  damped  oscillations  pro- 
duced by  the  discharge  of  a  condenser  across  a  spark  gap. 

One  great  advantage  obtained  by  the  use  of  undamped  waves  lies  in  the 
fact  that  when  transmitting  over  long  distances,  where  the  daylight  absorp- 
tion is  great  and  a  long  wave  length  is  desirable,  the  daylight  absorption, 
if  the  wave  length  be  over  3000  meters,  is  much  less  with  an  undamped 
wave  than  with  a  damped  wave.* 

The  frequency  of  these  oscillations  is  controlled  by  the  electrical  char- 
acteristics (capacity  and  inductance)  of  the  shunted  circuit.  When  this 
latter  consists  of  an  antenna  and  ground,  continuous  or  undamped  waves 
are  radiated. 

As  previously  explained  undamped  oscillations  are  generated  in  a  circuit 
containing  inductance  and  capacity  shunted  about  an  arc.  To  obtain  the 
high  frequency  oscillations  required  in  practice  an  arc  between  a  copper 
anode  (+ electrode)  and  a  carbon  cathode  (—electrode)  taking  about  500 

*  Austin,  Bui.  Bur.  Stds.,  Vol.  7,  p.  341,  the  formula  for  daylight  transmission 
of  Damped  Waves  is 


where 


7g  =  Sending  antenna  current  in  amperes. 

If  =  Received  antenna  current  in  amperes, 

Til  =  Effective  height  of  antenna  in  kilometers,  transmitting, 

hi  =  Effective  height  of  antenna  in  kilometers,  receiving, 

X  =  Wave  length  in  kilometers, 

d  =  Distance  in  kilometers, 

a  =  Daylight  absorption  coefficient  =  15  X  10'^ 

Fuller,  "  The  Effect  of  Wave  Length  on  the  Absorption  of  Undamped  Waves  " 
gives 

Ir  =  4.20      ^^      e      \i.5, 

where  all  characteristics  retain  the  same  meaning,  except  that  /3  =  45  X  10"*. 
This  formula  is  derived  from  actual  daylight  tests  made  between  San  Francisco 
and  Honolulu  over  a  period  of  six  months. 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  121 

volts  is  used.  The  arc  is  enclosed  in  an  air-tight  chamber  kept  filled  with 
a  gas  containing  hydrogen.  This  hydrogen  vapor  is  obtained  by  allowing 
alcohol  to  drip  into  the  arc  chamber.  A  strong  magnetic  field  is  established 
across  the  arc  by  two  coils  in  series  with  the  arc  circuit.  The  copper 
electrode  is  water  cooled. 

The  Federal  Telegraph  Company  has  developed  this  method  of  radio 
transmission  and  has  in  commercial  operation,  day  and  night,  stations  at 
Honolulu,  San  Francisco  and  other  points.  The  distance  from  Honolulu 
to  San  Francisco  is  2100  nautical  miles  and  the  100-kilowatt  equipment 
of  these  stations  is  similar  to  that  being  installed  by  this  company  at  Darien 
in  the  Panama  Canal  Zone,  for  the  Navy  Department. 

Other  stations  use  30-kilowatt  sets,  such  as  the  Navy  Department  is 
placing  at  Boston,  Mass.;  Point  Isabel,  Texas;  New  Orleans,  La.; 
Guantanamo,  Cuba,  and  the  Great  Lakes,  while  12-kilowatt  and  5-kilowatt 
sets  are  made  for  ships  and  smaller  land  stations. 

The  wiring  diagram  and  photograph  of  the  30  K.  W.  set,  figs,  62a  and 
62b,  are  typical  of  arc  sets. 

THE  ANTENNA. 

The  antenna  at  south  San  Francisco  is  supported  by  three  guyed  wooden 
towers,  placed  in  a  triangle,  one  of  608  feet  and  two  of  440  feet  in  height, 
and  is  of  the  flat-top  type.  Its  capacity  is  0.010  microfarad,  with  a  natural 
period  of  2300  meters,  and  an  efi:ective  height  of  approximately  425  feet. 

The  insulation  of  the  antenna  from  the  towers,  and  also  that  of  the  guys 
(which  are  insulated  every  100  feet  of  length)  is  composed  either  of  long 
wooden  breaks  or,  in  the  case  of  the  608-foot  tower,  of  stone  blocks,  10 
inches  x  10  inches  x  10  inches  in  size. 

THE  GROUND. 

This  is  a  radial  network  of  wire  extending  beyond  the  projected  area  of 
the  antenna  on  the  earth. 

THE  HELIX,   WAVE-CHANGING   SWITCHES,   ETC. 

The  antenna  lead  is  brought  with  suitable  insulation  to  a  switch  for 
transferring  the  antenna  from  the  sending  to  the  receiving  circuits.  The 
sending  inductance  is  a  helix  of  1-inch  copper  tubing,  52  inches  in 
diameter,  and,  in  the  case  of  the  Darien  installation,  16  feet  6  inches  long. 

The  cathode  terminal  of  the  arc  being  grounded,  the  anode  is  con- 
nected through  a  hot-wire  ammeter  to  a  number  of  wave-changing 
switches.  Any  one  of  these  may  be  made  to  engage  clips  connected  to 
points  on  the  helix,  giving,  according  to  the  number  of  turns  utilized,  a 
great  range  of  wave  lengths. 

No  condensers  are  used. 


122 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


Hh 


HHi 


H 


-^i 


y^ 


CO    -  1 

-i-_JI I— j»- 


mm, 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  123 

SIGNALS  AND  KEYS. 

In  this  system  the  oscillations  in  the  antenna  are  continuously  pro- 
duced by  the  arc,  therefore  the  signals  are  not  made  by  completely  break- 
ing this  oscillatory  circuit,  but  by  making  a  small  change  in  wave  length. 

This  change  is  made  by  short  circuiting  part  of  the  transmitting  in- 
ductance by  means  of  a  multiple  contact,  solenoid  operated  relay  key  of 
rugged  construction,  capable  of  handling  the  heavy  currents  necessary  to 
be  broken.    The  contacts  are  cooled  by  an  air  blast. 

The  current  in  the  key  solenoid  is  made  and  broken  by  a  "  key  con- 
troller." This  consists  of  two  copper  contacts  in  a  sound-proof  chamber, 
operated  in  a  magnetic  field  in  order  to  reduce  arcing  between  them.  One 
contact  is  moved  by  a  second,  exterior,  solenoid,  and  this  in  turn,  by  a 
small  current  and  an  ordinary  Morse  telegraph  key.  The  speed  obtainable 
with  this  relay  key  is  greater  than  that  of  the  fastest  hand  sending. 

If  it  be  desired  to  render  signals  audible  on  ordinary  "  spark  "  receiving 
apparatus  using  crystal  detectors,  and  the  like,  a  "  chopper  "  is  inserted  in 
the  key-antenna  circuit,  this  being  merely  a  rotary  means  of  changing  the 
continuous  oscillations  into  wave  trains  of  audible  frequency. 

THE  ARC. 

The  arc  itself  is  maintained  in  a  water-cooled,  air-tight  chamber,  within 
a  strong  magnetic  field  and  in  an  atmosphere  of  hydrogen  vapor. 

Means  are  provided,  either  by  a  spring  lid  or  a  poppet  valve  in  the 
chamber,  for  releasing  any  undue  pressure  caused  by  striking  the  arc  in 
an  explosive  mixture  of  air  and  hydrocarbons. 

The  cathode  electrode  is  of  carbon,  readily  replaceable,  and  is  rotated 
constantly  while  the  arc  is  in  operation,  in  order  to  keep  its  erosion  even 
and  the  arc  steady.  The  distance  between  it  and  the  anode  is  regulated 
either  by  hand  or  motor  control. 

The  anode  is  copper,  water  cooled ;  both  it  and  the  cathode  being  suitably 
insulated  from  the  arc  chamber. 

The  necessary  atmosphere  of  hydrogen  is  supplied  by  introducing  into 
the  chamber  ordinary  illuminating  gas,  alcohol,  ether,  water,  steam  or 
other  compounds  containing  hydrogen. 

Projecting  through  the  sides  of  the  chamber  are  the  poles  of  two  power- 
ful electromagnets,  in  the  field  of  which  the  arc  is  maintained.  These  are 
connected,  either  in  series  or  parallel,  to  the  jjower  supply  to  the  arc, 
usually  500  volts  direct  current. 

Choke  coils  are  inserted  in  the  power  leads  to  protect  the  latter  from  high 
frequency  current. 

A  starting  resistance  is  provided  to  take  care  of  the  momentary  short 
circuiting  of  the  power  line  caused  by  striking  the  arc.  This  resistance  is 
rapidly  cut  out  when  the  arc  is  established.  The  same  result  may  be  accom- 
plished by  striking  the  arc  at  a  low  voltage  and  raising  the  same  sub- 
sequently to  full  power. 


134  MANUAL    OF   RADIO    TELEGRAPHY    AND   TELEPHONY. 


Fig.  62b.— 30  K.  W.  Arc  Set. 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


125 


In  practice,  in  the  case  of  the  lOO-kilowatt  arc,  the  operations  of  turn- 
ing on  or  off  of  cooling  water,  gas  or  alcohol ;  of  starting  and  stopping  the 
carbon  drive,  blower,  tikker  motors,  etc.,  are  all  done  automatically  upon 
starting  and  stopping  the  arc,  the  latter  being  struck  and  its  length  ad- 
justed by  remote  control  also.  The  operating  room  is  usually  entirely 
separate  from  that  containing  the  arc  and  accessories. 

RECEIVING. 

In  receiving,  owing  to  the  accurate  tuning  obtainable  with  undamped 
waves,  a  very  loose  coupled  (and  therefore  highly  selective)  circuit  is  used. 


^J^/7/7<:^ 


IS    II 


l^r/aJp/(^  Cj2r7<:^f&'\izl  '^  1^r/}:P/77^/kr- 


7/}^/^&r 


^C. 


Fig.  62c. — Elementary  Poulsen  Receiving  Circuit. 


An  elementary  diagram  of  the  connections  for  the  receiving  circuit  is 
shown  in  fig.  62c.  The  variometer  being  used  to  vary  the  wave  length 
when  long  waves  are  being  received,  and  the  condenser  is  used  to  adapt  the 
antenna  for  the  reception  of  short  waves. 


186  MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 

The  Federal-Poulsen  tikker,  the  device  rendering  audible  in  the  tele- 
phone undamped  oscillations  received  by  the  antenna,  consists  of  a  revolv- 
ing brass  disc  upon  which  lightly  impinges  a  fine  steel  wire  and  is  very 
sensitive,  the  received  watts  in  the  antenna  necessary  for  unit  audibility 
(or  where  the  dots  and  dashes  of  signals  can  just  be  differentiated)  being 
3.2  10"^°  watts.  Metals  other  than  brass  and  steel  may  be  used.  The  ele- 
mentary diagram  fig.  62c  shows  the  location  of  tikker  in  the  receiving 
circuit. 

WIRELESS  TELEPHONE  TRANSMITTERS. 

183.  A  method  of  arranging  the  arc  circuit  for  wireless  telephony  is 
shown  in  fig.  62.  Here  the  arc  creates  the  continuous  undamped  oscilla- 
tions which  are  necessary  for  wireless  telephony.  The  telephone  trans- 
mitter in  the  aerial  modifies  (by  its  change  of  resistance  when  spoken 
into)  the  amplitude  of  successive  oscillations  in  accordance  with  the 
vibrations  of  the  sounds  of  the  voice.  These  produce  similar  variations  ia 
the  receiver  oscillations  and  thus  reproduce  speech.  It  has  been  im- 
practicable up  to  tlie  present  time  to  obtain  carbon  transmitters  which  can 
successfully  carry  large  oscillating  currents  and  vary  them  so  as  to  reli- 
ably reproduce  speech  at  long  distances.  On  this  account,  the  develop- 
ment of  wireless  telephony  has  been  retarded. 

The  undamped  oscillations  are  of  too  high  frequency  to  produce  sound, 
but  their  slow  variation  produces  sound.    (See  art.  201.) 

Assume  that  the  undamped  oscillations  have  a  frequency  of  700,000 
and  the  notes  of  the  human  voice  vary  through  two  octaves  (say 
from  300  to  1200  vibrations  per  second).  The  vibrations  of  the  tele- 
phone diaphragm,  by  changing  the  resistance  of  the  carbon,  modifies 
the  oscillating  current  in  the  aerial  (and  therefore  the  amplitude  of  the 
electric  waves  generated)  in  accordance  with  the  vibrations  of  the  voice  of 
the  person  speaking.  The  ordinary  receiving  circuit  having  a  crystal  or 
electrolytic  detector  serves  as  well  for  undamped  oscillations  as  for 
groups  of  wave  trains,  transforming  the  modified  oscillations  into  human 
speech  in  the  receiving  telephone. 

The  limit  of  mechanical  or  air  vibrations  recognized  as  sound  is  be- 
tween 30,000  and  40,000  per  second.  Although  the  undamped  oscilla- 
tions are  of  a  much  higher  frequency  and  therefore  produce  no  sound  in 
themselves,  modifications  of  the  amplitude  of  successive  waves  may  be  of 
such  a  nature  as  to  produce  sound  by  slower  variations  in  the  rise  and  fall 
of  the  received  current. 

The  transmitting  telephone  may  be  in  the  arc  circuit  instead  of 
the  aerial  as  shown,  or  it  may  be  inductively  connected  to  either  the  open 
or  closed  circuit.  There  is  as  yet  no  standard  practice.  The  telephone 
transmitters  are  specially  constructed  to  stand  the  voltage  and  current 
induced  in  the  aerial  or  in  the  closed  circuit. 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  127 


Fig.  62d.— Radio  Telephone  Set. 


128  MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

LIMITATIONS  ON  WAVE  LENGTHS. 

184.  A  certain  amount  of  inductance  is  necessary  in  the  closed  circuit 
in  order  to  transfer  energy  to  the  open  circuit,  whether  the  circuits  are 
direct  or  inductively  coupled.  Since  condensers  of  any  desired  capacity 
can  readily  be  obtained,  it  is  easy  to  make  the  closed  circuit  any  electrical 
length  we  desire. 

There  is,  however,  a  lower  limit  to  this,  depending  on  the  material  and 
arrangement  of  the  condenser  and  leads.  Other  things  being  equal,  the 
larger  the  capacit}^  the  longer  the  connecting  leads;  and  the  shortest 
wave  length  that  can  be  obtained  for  a  given  capacity  is  that  found  when 
the  leads  from  the  condenser  are  connected  in  the  most  direct  manner  to 
those  from  the  closed  circuit  and  spark  gap. 

The  standard  wave  length  for  ships  and  shore  stations,  using  damped 
waves,  was  first  set  at  320  meters.  It  is  now  600-1000  meters  for  ships. 
Much  longer  wave  lengths  are  used  for  undamped  wave  signalling. 

Experience  shows  that  aerials  with  short  wave  lengths  radiate  more 
efficiently  than  those  with  long  ones,  and  that  up  to  several  hundred 
miles  short  waves  travel  over  salt  water  with  no  great  absorption. 

When  transmission  over  land  is  necessary  and  for  long  distances  over 
water  we  gain  more  by  the  reduced  absorption  of  long  waves  than  we  lose 
by  decreased  radiation  efficiency. 

185.  The  open  circuit,  while  it  has  concentrated  inductance  like  the 
closed  circuit,  has  distributed  capacity  which  is  comparatively  small,  and 
though  any  electrical  length  we  desire  can  be  obtained  by  adding  induc- 
tance, it  is  found  that  concentrated  inductance  beyond  that  necessary  to 
receive  energy  from  the  closed  circuit  lessens  the  radiation,  and  on  that 
account  it  is  necessary  to  increase  the  period  of  the  open  circuit  by  adding 
capacity  in  the  shape  of  additional  wires  to  the  aerial.  We  have  seen 
that,  unless  they  are  quite  a  distance  apart,  two  parallel  wires  do  not  have 
twice  the  capacity  of  one,  so  that  it  is  practically  difficult  to  get  very  long 
wave  lengths  in  the  open  circuit,  especially  on  shipboard. 

The  wave  lengths  that  we  can  efficiently  use  in  the  open  circuit  are, 
therefore,  limited  by  practical  considerations. 

Since  the  energy  in  any  discharge  varies  as  the  square  of  the  voltage, 
and  since  any  desired  voltage  can  readily  be  obtained,  the  work  that  can 
be  stored  in  a  condenser  of  given  capacity  depends  only  on  the  dielectric 
strength  of  the  condenser  material. 

But  in  the  case  of  the  open  circuit,  when  the  first  transfer  of  energy  is 
completed,  unless  it  is  radiated  nearly  as  fast  as  received,  the  maximum 
voltage  in  the  open  circuit,  on  account  of  its  capacity  being  very  much 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  129 

smaller,  is  much  greater  than  that  in  the  closed  circuit.  And  we  find 
that  very  high  voltages,  on  account  of  difficulty  of  insulation,  break  out 
in  sparks  at  all  points  of  the  circuit,  that  the  aerial  wire  glows  through- 
out its  length,  and  the  whole  apparatus  generally  acts  like  a  dry  linen 
fire  hose  when  subjected  to  a  high  water  pressure — i.  e.,  it  spurts 
electricity  at  all  points  in  all  directions. 

So  practical  considerations  limit  the  wave  lengths  that  can  be  efficiently 
used  on  board  ship,  and  also  limit  the  power  that  can  be  used  with  them. 

186.  Eeferring  to  the  closed  circuit,  it  is  probable  that  the  best  results 
with  any  given  sender  are  obtained  when  the  work  necessary  to  charge 
the  condenser  to  the  transformer  voltage  is  equal  to  that  supplied 
by  the  available  power  of  one-half  alternation.  This  gives  but  one 
wave  train  per  alternation,  and,  if  true,  fixes  at  once  the  capacity  of 
the  closed  sending  circuits  for  any  given  power. 

OPEN   CIRCUIT — (aerial,   INDUCTANCE,   GROUND). 

187.  Aerials,  with  which  the  open  circuit  inductances  of  sending  sets 
are  connected,  are  shown  diagrammatically  in  figs.  63  to  71  inclusive. 

The  main  principles  to  be  remembered  in  connection  with  aerials  (or 
antennae,  as  they  are  sometimes  called)  are  that  the  higher  the  aerial  the 
more  efficiently  the  energy  will  be  radiated  in  the  form  of  electric  waves 
and  the  larger  the  currents  induced  in  the  vertical  part  of  the  aerial  the 
greater  the  amount  of  energy  radiated.  See  tables  9,  10,  11,  12,  appen- 
dix A. 

The  total  capacity  of  a  ship  aerial  is  usually  less  than  one  standard  jar. 
To  hold  the  same  amount  of  energy  as  the  condenser  circuit,  the  aerial 
is,  therefore,  while  oscillating,  charged  to  a  higher  maximum  potential 
than  the  closed  circuit. 

188.  The  form  of  aerial  now  generally  used  on  ships  and  ashore  is  called 
the  fat-top  or  inverted  L  (fig.  67). 

The  leads  to  the  operating  room  are  taken  from  one  end;  the  other 
(free)  end  is  subject  to  high  potentials  and  must  be  well  insulated. 

Some  T  aerials  are  in  use  (fig.  70).  They  give  greater  relative  capacity 
for  the  same  amount  of  wire;  but  T  aerials  sag  in  the  center,  thus 
decreasing  their  effective  height  and  they  are  subject  to  high  potentials 
at  both  ends. 

The  other  types  shown  are,  or  have  been,  used  on  shore  stations,  except 
the  special  receiving  aerial  shown  in  fig.  63,  which  is  the  direction  aerial 
used  on  ships  as  part  of  the  Bellini-Tosi  direction  finder  (art.  217). 

The  umbrella  aerial  shown  in  fig.  65  has  been  used  at  some  large 
shore  stations.    It  is  probably  the  best  form  that  can  be  supported  by  a 
single  mast. 
9 


130 


iMANUAL    OF    RADIO    TELEGUAPIIY    AND   TELEPHONY. 


K^SPAH 


FIG.    63    BELLINl-TOSI 


FIG.   64  MARCONI 


GOV3 


FIG.   65     UMBRELLA 


TO  SENDlNq  Ht\.\]k 
FIG    67 


auY9 


ne:         y     Mt 


stone:         t     massiel 
jnsulated  wire    4-  bare  wjrei 

FIG.    66 
(Now  Obsolete) 


TO  SENpjMCi  HELIX 


TO  SEMPlNCi  HELIX 


FIG.   68  FIG.   69 

(Now  Obsolete)  (Now  Obsolete) 


-TO  SENPlNGv  HELIX 
FIG.   70 


I  TO  SENDlNt^  HELIX 
FIG.    71 


Fig.  71a. — Latest  Marconi  High  Power  Antenna. 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY.  131 

Marconi  found  that  a  long  flat-top  aerial,  like  fig.  64  and  fig.  71a,  sends 
more  strongly  in  the  direction  away  from  the  free  end  of  the  aerial  and 
receives  more  strongly  from  the  direction  in  which  it  sends  best.  This  has 
proved  to  be  of  practical  use  on  shore,  where  the  horizontal  part  can  be 
made  very  long  as  compared  with  the  vertical  part  and  in  his  transatlantic 
stations  his  transmitting  aerials  are  installed  pointing  away  from  one 
another  and  the  receiving  aerials  (which  are  outside  of,  or  at  a  distance 
from,  the  transmitting  aerials)  are  also  very  long  (1  mile)  horizontally. 
No  satisfactory  explanation  of  the  directive  action  has  yet  been  given. 

189.  It  will  be  noted  that  the  diagrams  of  receiving  sets  (figs.  81  and 
82)  show  an  aerial  in  the  form  of  a  loop,  beyond  three  spark  points 
arranged  in  the  form  of  a  triangle.  The  lower  one  of  these  points  was  con- 
nected to  the  sending  circuit  inductance  so  that  as  far  as  sending  is 
concerned  this  aerial  was  the  same  as  any  other,  since  the  high  potentials 
used  in  sending  easily  jump  the  short  gaps  between  the  two  sides  of  the 
loop ;  but  for  receiving  it  was  different — the  weak  currents  can  not  jump 
the  gap,  which  is  known  as  an  anchor  spark  gap,  so  that  the  circuit  was 
only  looped  for  receiving  and  not  sending. 

The  anchor  spark  gap  served  to  cut  out  the  sending  circuit  when 
receiving.  When  sending,  the  volume  and  color  of  the  sparks  in  the 
anchor  gap  indicated  roughly  whether  the  sending  apparatus  was  work- 
ing properly.  For  receiving  sets  not  requiring  a  looped  circuit  the 
two  sides  of  the  loop  were  joined  below  the  gap  and  used  as  a  single  wire. 
A  little  consideration  will  show  that  the  wave  length  of  a  loop  is  the  same 
as  that  of  half  the  loop  on  open  circuit.  A  loop  is,  however,  a  persistent 
oscillator.  Now  that  hot  wire  ammeters  are  installed  on  all  sets,  anchor 
gaps  are  no  longer  useful  and  are  not  supplied. 

190.  Except  where  they  pass  near  conducting  objects  or  through  decks, 
all  parts  of  the  aerial  wire  are  left  bare  on  account  of  the  lighter  weight 
and  smaller  surfaces  exposed  to  the  wind  as  compared  with  insulated 
wire.  The  size  of  wire  generally  used  is  made  up  of  seven  strands  of 
No.  20  B.  &  S.  phosphor  or  silicon  bronze  wire  or  monnot  metal  having 
fairly  high  elastic  strength. 

Stranded  wire  is  more  flexible,  and  the  materials  given  above  have 
fairly  good  conductivity  and  much  greater  elasticity  than  copper  wire. 
The  elasticity  prevents  permanent  elongation  and  sagging  after  being 
hauled  taut.  For  those  parts  of  the  aerial  which  pass  through  decks  and 
for  parts  near  decks  a  special  heavily  insulated  flexible  stranded  wire, 
called  rat-tail  wire,  is  used. 

191.  The  natural  wave  lengths  of  certain  aerials  of  the  flat  top  type 
(inverted  L  and  T  aerials,  figs.  67  and  70)  are  given  in  tabular  form 
below.  To  the  aerial  is  added  the  necessary  turns  on  the  open  circuit 
helix  to  bring  the  natural  wave  length  to  the  standard.    It  usually  requires 


132 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


a  number  of  turns  of  the  helix  or  spiral  to  do  this.  When  it  is  desired  to 
greatly  increase  the  sending  wave  length,  special  loading  coils  are  added  to 
the  open  circuit.  (See  figs.  45,  46  and  47.)  Since  the  closed  circuit  has 
large  capacity  and  small  self-induction  a  turn  or  more  of  inductance  added 
to  the  closed  circuit  makes  a  large  percentage  addition  to  its  self-induction 
and,  therefore,  to  its  wave  length.  But  the  open  circuit  has  small  capacity 
and  relatively  large  self-induction,  so  that  each  additional  turn  does  not 
make  such  a  large  percentage  addition  to  its  self-induction  and,  therefore, 
its  increase  of  wave  length  per  additional  turn  is  much  less  than  that 
of  the  closed  circuit.    (See  Adjustments,  Chapter  VIII.) 


Ship. 


Type. 


No. 

wires. 


Distance 
apart. 


Length  of 
flat  top. 


"Vertical 

length  of 

lead  to 

operating 

room. 


Total 
length. 


Natural 
wave 

(meters). 


Glacier T 

Mayflower T 

Dolphin 1 

Louisiana 1 

Chester 7 

Birmingham q 

Connecticut 1 

Maine T 


2  feet 
26  inchei 

2  feet 

3  " 


Baltimore 

Ouantanamo . 


4  feet 
4    '■ 


170  feet 

124  " 
140  " 
150  " 
160  " 
160  " 

125  " 
120  " 
130  " 


Inverted 
pyramid. 


82  feet 

132  " 

136  " 
129  " 

97  " 

90  " 

137  " 
120  " 
132  " 
200  " 


252  feet 

256  " 
276  " 
279  " 

257  " 
250  " 
262  " 
240  " 
262  " 


330 
360 
330 
426 
395 
385 
360 
330 
370 
900 


In  all  aerials  referred  to  above,  except  those  of  the  Maine  and  Baltimore, 
the  long  wave  contained  the  greater  amount  of  energy.  In  the  case  of 
these  two  aerials  the  greater  amount  of  energy  was  radiated  on  the  short 
wave.  The  law  now  requires  that  the  energy  in  the  lesser  wave  shall  not 
be  more  than  10  per  cent  of  that  in  the  greater. 

These  sets  (except  the  Shoemaker,  whose  closed  circuit  was  designed 
to  give  loose  direct  coupling  at  425  meters,  and  which  did  not  require  the 
use  of  the  aerial  loading  coil  for  425  meters)  had  no  direct  provision  for 
changing  the  wave  length  of  the  aerial  except  in  the  coupling  coil,  and, 
therefore,  when  coupled  gave  a  wider  variation  from  the  standard  wave 
length  than  the  Shoemaker  sets. 


OPEN  CIRCUIT  INDUCTANCE. 

192.  With  direct  coupling  the  open  circuit  inductance  forms  part  of  the 
same  helix  as  the  closed  circuit  inductance,  as  has  already  been  stated. 
(See  fig.  40.)  In  inductively  coupled  sets  the  open  circuit  helix  or  spiral 
is  movable,  so  that  the  coupling  can  be  varied  by  moving  the  entire 
coil  while  keeping  the  same  wave  length.    Provision  is  also  made  for  a 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


133 


Fia.  72.— Spiral  Inductance. 


Fig.  73.— Helix  and  Spark  Gap. 


134 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


srariable  connection  to  the  helix  so  that  the  wave  length  can  be  varied. 
(Figs.  42  and  43.) 

It  must  not  be  forgotten  that  varying  the  wave  length  of  either 
circuit  by  varying  the  inductance  of  the  coupling  coil  or  coils  varies  the 
mutual  induction,  as  well  as  the  self-induction,  and  also  the  coupling 
and  damping,  so  that  the  most  recent  sets — Fessenden  (fig.  45),  Tele- 
funken  (fig.  46),  Lowenstein  (fig.  47) — make  provision  for  varying  the 
wave  length  at  some  other  part  of  the  circuit  than  at  the  coupling  coil, 
or,  as  in  the  Lowenstein  sets,  for  automatically  moving  the  coils  so  as  to 
maintain  the  same  coupling  when  the  wave  length  is  varied.  These  out- 
side coils  are  called  loading  coils,  as  distinguished  from  the  coupling 


Fig.  74 


Wave  changer. 


coils,  by  means  of  which  energy  is  transferred  from  the  closed  to  the 
open  circuit  (and  vice  versa  in  sets  not  having  quenched  or  properly  air- 
cooled  gaps). 

The  method  of  building  the  Telefunken  variometer  coils,  shown  in 
fig.  46,  is  illustrated  further  in  fig.  74.  This  method  of  varying  the 
self-induction  of  a  circuit  has  the  advantage  of  not  having  any  dead  ends 
as  in  the  old  inductance  helices,  shown  in  fig.  73.  However,  the  vari- 
ometer shown  in  fig.  74  is  not  suitable  for  inductive  coupling. 

The  spiral  inductance,  shown  in  fig.  72,  is  suitable  for  both  direct  and 
inductive  coupling,  and  also  for  loading  coils.  It  is  convenient  to  manu- 
facture and  to  mount  and  is  coming  into  use  rapidly.  The  inductance 
shown  in  fig.  72  is  an  early  DeForest  type. 


MANUAL    OF    RADIO    TELEGRAPHY   AND   TELEPHONY, 


135 


The  common  method  of  shifting  wave  lengths  quickly  is  hy  means  of  the 
navy  standard  wave  changer.  A  simple  wave  changer  is  shown  in  Fig.  74a. 
The  coils  of  the  primary  and  secondary  circuits  are  mounted  in  such 
manner  in  the  wave-changer  that  by  a  simple  movement  of  one  handle 
the  inductance  of  both  couple  coils  and  loading  coils  is  varied  properly  to 
give  any  one  of  several  wave  lengths  for  which  the  apparatus  is  adjusted. 
The  wave  changer  is  the  invention  of  Mr.  Guy  Hill  and  G.  H.  Clark,  radio 
expert  aids  of  the  navy. 

AERIAL  ACCESSORIES. 

193.  A  lightning  switch  (fig.  75)  is  installed  outside  the  station,  or 
where  the  aerial  enters,  by  means  of  which  it  is  grounded  during  thunder 
storms. 


I  ^ 


Fig.  75.— Lightning  Switch. 


Fig.  76. — Hot  Wire  Ammeter. 


The  other  aerial  accessory — the  hot  wire  ammeter  (fig.  76) — is  in- 
stalled in  the  ground  lead;  its  uses  are  particularly  referred  to  Id 
Chapter  VIII. 


136  MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 

GROUNDS  AND  GROUND  CONNECTIONS. 

194.  As  has  been  previously  explained,  wireless  telegraphy  makes  use 
of  earthed  electric  waves,  as  compared  with  the  free  waves  discovered  by 
Hertz  and  used  by  Marconi  in  his  first  experiments.  It  was  soon  found 
by  Marconi  that  good  connection  to  earth  or  to  a  large  conducting  body 
is  essential  to  good  working.  On  board  ship  the  end  of  the  aerial  below 
the  open  circuit  inductance  (called  the  ground  had)  must  be  welJ 
soldered,  bolted,  or  clamped  to  some  portion  of  the  hull. 

A  grounded  vertical  wire,  well  earthed,  has  a  wave  length  not  less  thau 
four  times  its  natural  length.  At  its  free  end  there  is  a  potential  loop 
and  a  current  node  (maximum  potential — no  current).  At  its  earthed 
end  there  is  a  current  loop  and  potential  node  (maximum  current — no 
potential).  (See  fig.  18d.)  The  same  wire  free  at  both  ends  has  an 
electrical  period  equal  to  twice  its  length,  and,  if  oscillating,  has  high 
potentials  at  both  ends.  If  the  ground  connection  is  not  good,  there  is  a 
tendency  to  choke  the  current  passing  in  and  out  of  the  earth  and  thus 
to  cause  a  rise  of  potential  and  consequent  sparking  and  reflection  of 
energy  at  the  earth  connections,  making  the  period  irregular  and  impair- 
ing the  sending  qualities  of  the  station. 

It  should  be  possible  to  grasp  the  ground  lead  where  it  is  soldered  to 
the  ship  without  injury.  Inability  to  draw  a  spark  there  is  proof  of 
good  connection. 

195.  At  shore  stations  it  is  found  that  the  resistance  of  the  earth  be- 
tween two  earthed  conductors,  a  given  distance  apart,  varies  widely  in 
different  localities  and  even  in  the  same  locality  with  moisture  and  tem- 
perature. Low  ground  resistance  at  a  station  is  usually  accompanied  by 
good  radiating  qualities.  Where  and  when  the  soil  is  very  dry  it  is  neces- 
sary to  pay  much  greater  attention  to  the  area  of  the  ground  connections, 
and  where  the  resistance  of  the  earth  in  the  vicinity  of  the  station  is  high 
the  station  is  a  poor  radiator  unless  an  artificial  ground  called  a 
"  counterpoise  "  is  installed.  This  can  consist  of  any  large  conducting 
area  laid  on  the  ground  or  wires  connected  between  the  mast  guys.  The 
natural  period  of  the  counterpoise  should  be  the  same  as  that  of  the 
aerial.  The  U.  S.  Naval  Eadio  Station  at  Peking  has  its  mast  and  counter- 
poise about  50  feet  above  ground,  on  top  of  the  wall  of  the  Tartar  City. 
This  set  operates  with  fair  eflficiency. 

Generally  a  good  ground  is  made  by  connecting  the  ground  lead  to 
copper  plates  of  large  area  in  good  contact  with  moist  earth,  or  to 
radiating  lines  of  galvanized  iron  telegraph  wire  ending  in  pipes  driven 
to  moist  earth,  or  to  wire  netting  spread  on  the  ground  and  covered  with 
earth.  At  stations  on  tops  of  buildings  grounds  are  made  to  the  steel 
frames  of  the  building  and  to  water  and  gas  pipes. 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  137 

As  previously  stated,  Dr.  Austin  has  shown  that  the  high  frequency 
resistance  of  a  well-installed  ship  aerial  should  not  exceed  2  ohms  at  wave 
lengths  slightly  greater  than  twice  the  natural  period  of  the  aerial,  and 
should  not  increase  greatly  for  longer  wave  lengths. 

This  phenomenon  does  not  accord  with  theory  and  is  somewhat  compli- 
cated by  the  fact  that  we  have  no  absolute  means  of  measuring  the  true 
resistance  and  the  radiation  resistance  separately.  Their  resultant  is 
measured  as  a  single  quantity. 

We  want  the  apparent  resistance  due  to  radiation  of  energy  to  be  as 
high  as  possible  and  the  true  resistance  to  be  as  low  as  possible.  The  in- 
crease of  resistance  referred  to  above  is  not  accompanied  by  any  increase 
in  radiation.  It  is,  therefore,  believed  to  be  a  reaction  due  to  earth  cur- 
rents, in  the  same  way  that  other  aerials  or  circuits  having  the  same,  or 
nearly  the  same,  period  react  on  the  aerial  and  increase  its  apparent  re 
sistance  without  improving  the  radiation. 


Chapter  VII. 

EECEIVING  APPARATUS. 

196.  Receiving  and  detector  circuits  are  illustrated  in  figs.  77  to  92, 
inclusive. 

In  all  figures,  the  fixed  condensers  shown  are  for  the  purpose  of  pre- 
venting the  direct  current  from  the  battery  or  detector  from  flowing 
through  the  inductance.  Variable  condensers,  and  variable  inductances 
are  used  for  changing  the  period  (wave  length)  of  the  circuits. 

Referring  to  fig.  79,  the  cup-shaped  construction  under  the  word 
Pessenden  indicates  a  detector  and  the  construction  shown  above  the  fig- 
ures 79  indicates  a  telephone  in  all  diagrams.  The  non-inductance  resist- 
ance, with  arrow-headed  connection,  is  used  to  regulate  the  impressed 
voltage  at  the  detector  terminals.  It  is  called  a  potentiometer.  Other 
symbols  used  have  been  previously  described. 

197.  Fig.  77  shows  the  detector  (in  this  case  a  coherer — art.  211)  in 
shunt  in  the  open  circuit,  the  open  circuit  having  a  variable  tuning 
inductance.  The  remainder  of  the  figure  shows  the  coherer-tapper,  call, 
and  the  relay  for  the  Morse  recorder. 

Fig.  77,  like  figs.  78  and  79,  illustrates  direct-connected  receiving  sets. 
They  are  not  now  generally  used.  Inductively  connected  sets,  shown  in 
figs.  86  and  88  to  92,  are  preferred. 

Fig.  92  shows  a  method  of  connecting  both  loading  and  coupling  coils, 
which  avoids  dead  ends  and  inductive  effects  on  parts  in  circuit.  It  also 
shows  connections  for  putting  a  condenser  in  series  or  parallel  with  the 
aerial,  in  accordance  with  present  specifications. 

It  will  be  noted  that  in  fig.  83  provision  is  made  for  tuning  the  closed 
circuit  with  detector  directly  in  circuit;  while  in  the  Fessenden  interfer- 
ence preventer  illustrated  in  fig.  85,  no  provision  is  made  for  tuning  the 
detector  circuit. 

In  figs.  80  and  86  the  detector  is  in  shunt  around  a  closed  tuned  circuit. 

In  all  inductively  connected  receiving  sets,  provision  is  made  for  vary- 
ing the  mutual  induction  between  the  open  and  closed  circuits.  This 
whether  the  closed  circuit  is  tuned  or  untuned. 

Professor  Pierce's  investigations  of  detector  circuits,  like  those  in  fig. 
83  (except  that  the  closed  circuit  inductance  was  fixed  and  the  condenser 
variable),  indicate  that,  if  the  resistance  of  the  detector  is  not  too 
great,  very  much  greater  selectivity,  with  equal  loudness  of  signals,  is 
obtained  by  tuning  the  detector  circuit,  with  the  detector  directly  in  the 
circuit  as  in  fig.  83.  No  absolute  figures  are  at  hand  as  to  the  effect  of 
shunting  the  detector  around  a  closed  tuned  circuit  as  in  figs.  80  and  86. 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


139 


ELEMENTARY   DIAGRAMS,  RECEIVING,  AND  DETECTOR  CIRCUITS. 

Dc  Forest 

JL 


(Now  Obsolete) 
MASSIE 


^^ir 


1 


IK 


rjOSO^ 


^yOUQ^ 


^^ 


FIG.  81 
(Now  Obsolete) 


Shoemaker 


\/ 


ryOSMYJf. 


v^^ 


U 


=^ 


FIG.   82 
(Now  Obsolete) 


pWB 


FIG-   83 


140  MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 

but  results  obtained  in  distance  of  communication  show  this  method  equal 
if  not  superior  to  any  other,  and  it  would  seem  that,  if  the  detector  has  a 
resistance  such  as  would  prevent  sharp  resonance  from  being  obtained 
when  placed  directly  in  the  closed  circuit,  shunting  it  will  assist  in 
producing  sharp  resonance  and  together  with  tuning  the  closed  circuit 
make  a  more  efficient  arrangement.  It  is  now  the  usual  practice  to 
tune  the  closed  circuit  and  shunt  the  detector  around  it. 

198.  Eeceiving  sets,  such  as  shown  in  fig.  80,  were  first  introduced  by 
Stone  and  used  later  by  Marconi.  The  intermediate  tuned  circuit  in 
these  sets  is  called  the  weeding  out  circuit.  Provision  is  made  for  switch- 
ing the  detector  to  the  weeding  out  circuit  when  very  sharp  tuning  is 
unnecessary,  since  there  is  loss  of  range,  due  to  loss  of  energy  in  so  many 
transfers. 

The  Fessenden  interference  preventer,  shown  in  fig.  86,  attains  select- 
ivity in  a  different  manner  from  that  just  described.  The  currents 
induced  in  the  aerial,  from  whatever  cause,  have  two  possible  paths  to 
earth;  one  of  these  paths  is  tuned  to  the  wave  length  it  is  desired  to 
receive,  while  it  is  supposed  that  waves  of  other  lengths,  or  static  dis- 
charges, out  of  tune  with  either  leg,  will  divide  themselves  equally  be- 
tween the  two  legs  and  produce  no  effect  on  the  untuned  detector  circuit. 

Attention  is  invited  to  figs.  81  and  82,  showing  the  DeForest  and  Shoe- 
maker looped  receiving  circuits.  These  differ  from  the  other  circuits 
illustrated  in  that  the  induced  currents  are  in  the  same  direction  on  the 
two  sides  of  the  loop  and  like  a  double-ended  sending  aerial  induce  a 
maximum  potential  at  some  point  in  the  loop  whose  electrical  distance 
from  the  point  of  origin  of  the  disturbance  is  the  same  for  each  side. 
The  wave  length  of  a  looped  circuit  ungrounded  is  therefore  the  same  as 
that  of  one-half  of  it  ungrounded  and  the  wave  length  grounded  is  twice 
the  electrical  length  of  the  loop.  In  other  words,  one-half  the  loop  can 
be  considered  as  a  shunt  of  the  same  period  as  the  other  half.  From  this 
point  of  view  the  DeForest  detector  circuit  is  practically  the  same  as 
fig.  83  and  the  Shoemaker  circuit  can  be  considered  as  one  having  a 
detector  directly  in  the  open  circuit  and  shunted  by  a  variable  con- 
denser. 

199.  The  variable  inductance  of  fig.  83  is  hinged  so  that  the  coupling 
can  be  varied  by  a  combined  movement  of  separation  and  rotation  with 
reference  to  the  fixed  inductance  (fig.  100). 

In  fig.  86  the  coupling  is  varied  by  sliding  the  closed  circuit  inductance 
on  a  graduated  bar  parallel  to  its  axis  (fig.  101a). 

Figs.  84  and  88  represent  the  valve  and  audion  receiving  circuits.  In 
fig.  84,  the  valve  detector  is  shown  as  shunted  around  a  tuned,  closed 
circuit.  The  audion  shown  in  fig.  88  has  tuned  connections  like  the 
valve  detector,  but  has  a  local  battery  in  the  telephone  circuit. 


MANUAL   OF   RADIO    TELEGRAPHY    AND   TELEPHONY.  141 


i,    TO  AERtAL 


y.-c 


oaflfiOyHMiS 


FIG.  84   l/ALVE   RECEIVER -MARCDN I - 


TO  AERIAL 

VMRELESS    SPECIALTY 
APPARATUS    CO. 


FIG.  85    FES5EUDZN     INTERFERENCE  PREVENTER 


TO  AERIAL 


-h^ 


m 


€^ 


D=ie 


Fig.  87. — Magnetic  Detector — Marconi. 


142 


MANUAL   OF   RADIO    TELEGRAPHY   AND   TELEPHONY. 


Fig.  92  represents  circuits  of  a  receiving  set  complying  with  present 
specifications.  In  all  such  sets  closed  circuits  are  calibrated  and  curves 
drawn  or  a  scale  furnished  showing  wave  lengths  for  all  settings  from  200 

A 


Fia.  88. — Audion. 


to  4000  meters,  and  additional  calibrated  loading  coils  for  very  long  waves 
are  supplied. 

With  very  loose  coupling  the  wave  length  of  received  signals  can  thus  be 
read  directly. 

200.  Fig.  89  represents  receiving  circuits  for  continuous  oscillations; 
it  shows  the  receiving  telephone  connected  across  the  terminals  of  a  fixed 
condenser  in  series  with  the  detector. 


Fig.  89.— Federal  Co    (Poulsen) 


In  using  undamped  oscillations  for  wireless  telegraphic  purposes  it 
must  be  remembered  that  the  frequency  of  the  oscillations  themselves  is 
too  high  to  be  heard  in  the  telephone  connected  with  the  ordinary  re- 
ceiving circuit,  and  when  the  circuit  at  the  sending  station  is  closed  all 
that  would  be  heard  is  a  slight  click,  so  that  there  is  no  way  of  telling  a 


MANUAL   OF   RADIO    TELEGRAPHY   AND   TELEPHONY.  143 

dot  from  a  dash.  This  makes  it  necessary  to  place  a  rapidly  rotating 
circuit  breaker  either  in  the  sending  or  the  receiving  circuit  for  the  pur- 
pose of  creating  a  buzz  in  the  telephone  at  the  receiving  station  when  the 
sending  circuit  is  closed.  This  circuit  breaker  may  be  placed  in  the  send- 
ing aerial,  while  the  sending  key  is  placed  either  in  the  aerial  or  shunted 
around  a  few  turns  of  the  aerial  inductance,  in  which  case  it  serves  merely 
to  throw  the  aerial  in  and  out  of  tune.     (Art.  164.) 

If  no  interrupter  is  used  in  the  sending  apparatus,  no  signals  can  be 
read  at  a  receiving  station  unless  the  wave  trains  are  there  broken  up  so 
as  to  produce  a  buzz  in  the  telephone.  For  this  purpose  the  Poulsen  ticker 
is  sometimes  used,  whicli  at  tlie  same  time  does  away  with  the  need  of  any 
special  receiver.  It  consists  essentially  of  a  circuit  breaker  actuated  by  a 
small  magnetic  vibrator,  kept  in  action  by  a  dry  cell.  In  this  receiver  the 
closed  circuit  is  coupled  very  loosely  to  the  aerial,  and  this  circuit  is  inter- 
mittently connected  to  a  large  condenser,  of  the  order  of  a  microfarad,  by 
the  ticker  or  a  slipping  contact  detector  (fig.  89).     (Art.  210.) 

During  the  time  of  contact  the  condenser  becomes  charged,  and  when 
the  contact  is  broken  it  discharges  itself  through  the  telephone,  producing 
a  note  corresponding  in  tone  to  the  frequency  of  the  ticker. 

201.  Figs.  90  and  91  represent  a  Fessenden  receiving  set  and  hetero- 
dyne, respectively,  the  loop  in  the  aerial  being  for  the  purpose  of  impress- 
ing the  oscillations  in  the  heterodyne  circuit  on  the  aerial  and,  conse- 
quently, on  the  closed  receiving  circuit. 

As  will  be  seen  from  an  inspection  of  fig.  91,  the  heterodyne  is  an  arc 
sending  set,  without  aerial  and  with  variable  inductances  in  the  closed 
circuit  for  changing  its  wave  length  and  the  frequency  of  the  continuous 
oscillations  it  produces. 

The  heterodyne  is  valuable  as  a  means  of  enabling  us  to  read  signals 
sent  with  undamped  oscillations,  without  using  an  interrupter  at  the  send- 
ing end  or  a  ticker  at  the  receiving  end.  It  is  also  useful  as  an  amplifier 
of  signals  from  damped  oscillations. 

The  undamped  oscillations  in  the  receiving  aerial  produced  by  the 
heterodyne  are  combined  with  those  from  the  transmitting  aerial.  If 
they  are  of  exactly  the  same  frequency,  they  simply  tend  to  amplify  or 
neutralize  each  other,  depending  on  their  relative  phases.  If  not  of  the 
same  frequency,  beats  are  produced  as  in  music.  For  instance,  if  the  trans- 
mitter has  a  frequency  of  300,000  per  second  and  the  heterodyne  301,000, 
when  one  has  made  300  vibrations  the  other  will  have  made  exactly 
301 ;  so  that  they  will  exactly  coincide  once  in  each  j-^  second,  thus  pro- 
ducing a  third  frequency  of  1000  per  second.  Both  transmitter  and 
heterodyne  have  a  frequency  much  greater  than  can  be  detected  by  the 
human  ear,  but  their  combination,  producing  a  maximum  of  current  in 
the  aerial  1000  times  per  second,  can  be  read  easily.     The  resultant 


144 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


frequency  would  be  the  same  (1000)  if  the  frequency  of  the  heterodyne, 
were  299,000.  If  it  were  302,000,  the  transmitter  would  make  150  vibra- 
tions while  the  heterodyne  made  151.  They  would  coincide  2000  times 
per  second  and  the  resultant  note  in  the  receiving  telephone  would  have 
that  frequency. 


Fig.  90. — Fessenden. 


SOO    VOI-TS   DC 


Fig.  91. — Fessenden  Heterodyne. 


We  see,  therefore,  that  by  varying  the  heterodyne  by  means  of  the 
variable  condensers  shown  in  fig.  91,  we  can  produce  any  desired  note  at 
the  receiving  station. 

It  is  not  necessary  that  the  heterodjTie  should  be  in  the  same  room  or 
even  in  the  immediate  vicinity  of  the  receiving  aerial.  Two  stations,  miles 
apart,  sending  continuous  oscillations,  may  heterodyne  each  other,  if 
one  is  sending  while  the  other  is  receiving. 

As  an  accessory  of  the  receiving  apparatus,  the  heterodyne  promises  to 
be  very  valuable.  The  positive  electrode  is  copper  and  the  negative 
electrode,  carbon ;  the  same  as  in  the  ordinary  arc  transmitter. 

Ammeters  are  supplied  with  it  for  indicating  the  current  in  both  the 
primary  and  oscillating  circuits.  Thus  far,  the  best  results  in  operation 
are  obtained  by  keeping  the  readings  of  the  two  ammeters  as  nearly  equal 


MANUAL   OF   RADIO    TELEGKAPHT   AND   TELEPHONY. 


145 


as  possible.  With  properly  adjusted  carbons,  the  instrument  should 
operate  an  hour  without  attention  and  then  requires  only  the  careful 
cleaning  and  facing  up  of  the  carbons. 

202.  In  spark  sets  we  want  the  sending  aerial  to  be  a  good  radiator,  but 
not  so  good  that  it  will  give  a  whip  crack  discharge.  We  want  its  oscilla- 
tions to  be  persistent  enough  to  require  for  their  best  reception  a  receiving 
aerial  tuned  to  the  period  of  the  sender,  and  as  a  present  standard  we 
have  set  for  the  sender  a  damping  considerably  lees  than  .2,  so  that  it 
makes  fifteen  complete  oscillations  before  the  oscillating  current  falls  to 
.1  of  its  original  value.    We  want  the  receiving  aerial  to  radiate  as  little 


UOADIMG      COIl-S 


^^<^ 


Fio.  92. — Standard  Receiving  Set. 


as  possible;  but  to  so  combine  the  energy  of  the  fifteen  waves  that  the 
highest  maximum  is  produced  in  the  aerial,  and  transferred  to  the  closed 
receiving  circuit. 

If  the  sending  aerial  is  coupled  so  as  to  send  out  waves  of  two  lengths, 
there  appears  to  be  no  question  that  the  coupling  of  the  receiving  circuits 
should  be  such  that,  if  they  acted  as  senders,  they  would  send  out  waves 
of  these  lengths,  or  so  loosely  coupled  that  their  natural  period  is  that  of 
the  arriving  wave  containing  the  most  energy.  If,  in  the  case  of  very 
loosely  coupled  circuits  or  those  supplied  with  quenched  spark  gaps,  but 
one  wave  length  is  being  radiated,  receiving  circuits  should  also  be 
loosely  coupled  or  should  be  coupled  so  that  the  transfer  of  energy  from 
the  open  to  the  closed  circuit  and  the  damping  of  the  latter  (with  the 
detector,  however  connected)  is  at  such  a  rate  that  a  maximum  current 
in  the  closed  circuit  is  reached  at  the  instant  the  open  circuit  has  come 
10 


146  MANUAL   OF   RADIO    TELEGRAPHY   AND   TELEPHONY. 

to  rest  after  being  set  into  vibration  by  the  passing  wave  train  and  after 
having  radiated  or  transferred  all  its  induced  energy.  This  is  analogous 
to  the  statement  relative  to  the  quenching  of  the  closed  sending  circuit 
(throwing  it  out  of  tune)  when  the  open  circuit  has  reached  its  first  maxi- 
mum. When  the  closed  circuit  has  reached  its  first  maximum  the  rectified 
current  in  the  case  of  crystal  detectors  or  the  battery  current  in  the  case 
of  electrolytic  detectors  has  also  reached  its  maximum. 

It  must  be  remembered  that  change  of  coupling  changes  mutual  induc- 
tion and,  therefore,  changes  the  tune  so  that  retuning  is  necessary  after 
every  change  of  coupling. 

NAVY  RECEIVING  SET  TYPE  A. 

Coupling. — This  receiver  differs  from  all  earlier  sets  in  the  naval  service 
in  that  there  is  no  electromagnetic  coupling  between  the  primary  and  sec- 
ondary circuits. 

In  the  ordinary  type  of  set,  the  primary  and  secondary  coils  are  electro- 
magnetically  coupled,  and  the  coupling  is  "increased"  by  moving  the 
coils  closer  to  each  other,  and  "  decreased  "  by  separating  the  coils.  In 
this  type,  the  inductances  in  the  primary  and  secondary  systems  are  placed 
at  right  angles  to  each  other,  so  that  there  is  no  mutual  induction  between 
them,  and  the  coupling  is  obtained  by  means  of  small  variable  condensers 
connecting  the  two  systems.  Here,  to  increase  the  coupling,  a  greater 
value  of  the  coupling  condenser  is  used,  and  vice  versa.  The  inductances 
are  not  moved  at  all,  but  are  permanently  located. 

The  "  coupling  condenser  "  acts  as  a  sort  of  "  energy  controller  "  or 
"  valve  "  between  the  two  systems  (primary  and  secondary) .  The  greater 
the  value  of  this  condenser,  the  more  energy  is  transferred  from  the 
antenna  circuit  to  the  detector  circuit,  and  conversely.  In  this  respect  the 
analogy  with  the  electromagnetic  coupling  method  holds,  but  in  other  ways 
there  seems  to  be  a  difference. 

It  is  interesting  to  note,  from  the  theoretical  standpoint,  that  the  same 
effect  can  be  produced  if  an  inductance,  or  even  a  resistance,  be  used  in 
place  of  the  "  coupling  condenser,"  but  the  efficiency  is  very  much  less  than 
with  the  condenser. 

The  chief  advantages  of  the  "  static  "  or  "  condenser  "  coupling  over  the 
electromagnetic  method  are : 

(a)  Compactness  of  Set. — It  is  not  necessary  to  separate  the  induc- 
tances to  decrease  coupling.  For  very  loose  coupling,  with  the  old  type  of 
set,  it  was  necessary  to  move  the  secondary  coil  quite  a  distance  from  the 
primary.    Here,  the  coils  are  fixed  in  position. 

(b)  Ease  of  Operation. — With  electromagnetically  coupled  sets,  the 
mechanical  movement  of  the  secondary  coil  always  proved  rather  bother- 
some, especially  when  quick  changes  in  coupling  were  necessary.  This  is 
obviated  by  the  extremely  easy  operation  of  the  coupling  condenser. 


MANUAL  OF   RADIO   TELEGRAPHY   AND  TELEPHONY.  147 

(c)  Increased  Efficiency  of  Inductances. — In  the  old  type,  it  was  neces- 
sary to  wind  the  inductances  in  such  a  form  that  there  would  be  sufficient 
coupling  under  any  circumstances.  This  resulted  in  the  cylindrical  form 
being  of  necessity  adopted,  A  much  more  efficient  form  of  winding  is 
adopted  in  the  present  sets,  the  "  banked  "  winding  for  some  of  the  coils, 
and  the  "  square  section  "  method  for  others. 

(d)  Increased  Over-All  Efficiency  of  Receiver. — The  electrostatic  coup- 
ling gives  equal  efficiency  to  electromagnetic  for  short  wave  lengths,  and 
very  much  greater  for  long  wave  lengths. 

(e)  By  a  simple  switching  device,  a  "  stand-by  "  or  "  pick-up  "  circuit 
greatly  superior  to  any  heretofore  developed  can  be  used.  This  pick-up 
circuit  enables  receiving  to  be  done  over  a  comparatively  wide  range  of 
wave  lengths.  Hence  the  sharpness  of  tuning  is  sufficient  for  ordinary 
"  pick-up  "  purposes  without  the  usual  defect  of  picking  up  every  signal 
and  disturbance  in  the  vicinity. 

This  receiver  also  contains  a  novel  indicating  mechanism,  whereby  the 
operator  can  set  the  receiver  in  advance  to  be  in  tune  with  any  desired  wave 
length.  This  is  very  important  for  battle  radio  work.  The  increased  use 
of  the  transmitter  wave  changer  renders  some  device  necessary  for  the 
receiver,  and  this  is  the  first  apparatus  to  contain  this  feature. 

The  method  commonly  in  use  for  setting  the  receiver  in  advance  to  a 
given  wave  length  consists  in  having  the  operator  refer  to  a  table  for  the 
proper  value  of  primary  coil  (tens  and  units),  primary  loading  coil, 
primary  condenser,  secondary  coil,  secondary  condenser,  and  coupling.  In 
this  form,  the  primary  can  be  adjusted  by  one  movement,  the  secondary  by 
another,  and  the  coupling  by  a  third.  Later  designs  will  probably  reduce 
these  movements  to  two,  the  primary  and  secondary  being  simultaneously 
adjusted  as  in  the  transmitter  wave  changer. 

In  this  connection  it  should  be  noted  that  in  the  transmitter  wave 
changer  all  three  variables,  i.  e.,  primary,  secondary,  and  coupling,  are 
varied  simultaneously.  In  this  case  the  damping  is  fixed,  being  the  damp- 
ing of  the  transmitter  set  itself.  In  the  receiver,  however,  the  damping  is 
determined  in  part  by  the  distant  transmitter  and  can  be  widely  different 
when  receiving  from  different  stations,  even  on  the  same  wave  length. 
Hence  it  is  not  practicable  to  make  all  three  adjustments  with  the  receiver 
by  one  movement.  The  coupling  must  always  be  independent,  to  enable 
adjustment  to  suit  the  local  conditions. 

Primary  Circuit  (see  fig.  92a). — This  consists  of  two  inductances  vari- 
able by  small  steps,  a  loading  inductance  and  series  condenser.  The  larger 
of  the  variable  inductances  (45-46)  has  a  total  value  of  1.2  M.  H.,  divided 
into  40  steps  of  equal  inductance  per  step.  (Note  that  the  divisions  are 
not  of  equal  numbers  of  turns,  but  of  equal  values  of  inductance.  This 
insures  constant  overlapping  between  sections.) 


148  MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


Fig.  92a. — Navy  Receiving  Set.    Type  A. 


MANUAL   OF   RADIO    TELEGRAPHY   AND   TELEPHONY.  149 

The  smaller  of  the  variable  inductances  (51-52)  has  a  total  value  of 
0.03  M.  H.,  divided  into  20  equal  steps.  Both  coils  are  wound  on  the  same 
core.    The  smaller  is  single  layer,  and  the  larger  is  wound  banked. 

The  loading  coil  (39-42)  has  a  total  value  of  6  M.  H.,  in  5  equal  steps. 
All  coils  are  wound  with  Litzendraht.  The  series  condenser  (7-8-9-10) 
may  have  three  values,  0.0009,  and  0.0015,  also  0.0003,  respectively. 

Secondary  Circuit. — The  secondary  coil  (16-24)  is  wound  in  the  same 
manner  as  the  larger  of  the  variable  inductances  in  the  primary  and  has  a 
total  of  3  M.  H.  There  are  six  steps,  all  but  the  first  and  second  being 
equal  and  of  value  0.6  M.  H.  The  secondary  variable  air  condenser 
(25-26)  is  of  the  balanced  type  and  has  a  total  capacity  of  0.0025  Mfd., 
with  a  total  value  of  .007  Mfd. 

'Potentiometer. — The  potentiometer  (61-75)  is  wound  with  No.  38 
German  silver  wire  with  a  total  resistance  of  400  ohms.  The  various  steps 
are  25-25-25-25-25-25-35-35-40-40-50-50  ohms,  respectively. 

Buzzer. — The  buzzer  (67-68)  for  testing  the  detector  is  of  the  Ericsson 
type,  and  is  mounted  with  thick  felt  on  the  top  of  the  panel. 

The  buzzer  control  key  (71-72)  enables  the  buzzer  to  be  left  in  con- 
tinuoue  operation,  giving  free  use  of  both  hands  for  other  adjustments,  or 
operated  intermittently  by  hand  as  desired.  A  key  (64-65)  controls  the 
potentiometer  battery  so  that  it  can  be  cut  off  when  the  set  is  not  in  use. 
Separate  batteries  are  used  for  the  buzzer  and  potentiometer  in  order  to 
obviate  false  signals  in  the  telephones.  The  buzzer  acts  inductively  on  the 
antenna  circuit,  as  shown  in  the  schematic  diagram,  so  that  it  not  only  can 
be  used  for  tests  for  sensitiveness  of  detector,  but  also  can  be  used  to 
indicate  approximately  whether  or  not  the  antenna  and  detector  circuits 
are  in  resonance  with  one  another. 

No  provision  is  made  for  detector  or  telephones  other  than  to  provide 
binding  posts  for  these  to  be  connected.  The  binding  posts  are  so  con- 
structed that  two  sets  of  telephones  can  be  connected  in  parallel  if  desired. 

Circuits  of  Receiver. — Fig.  92b  shows  the  schematic  representation  of 
the  two-circuit  electrostatically  coupled  receiver. 

The  primary  circuit,  Cj,  L^,  is  tuned  to  the  incoming  wave  length. 
Similarly,  the  secondary  coil  L2,  and  condenser  Co,  are  resonant  to  the 
same  wave  length.  The  energy  is  transferred  from  the  one  circuit  to  the 
other  by  means  of  the  "  coupling  condensers  "  00^  and  CC,.  These  con- 
densers are  in  no  sense  of  the  word  tuning  condensers,  and  do  not  vary  the 
adjustments  of  either  primary  or  secondary.  They  are  used  for  no  other 
purpose  than  their  name  implies. 

It  is  possible  to  use  only  one  condenser,  CCj,  the  connection  from  ground 
to  the  secondary  system  being  by  a  direct  wire  (CC,  short  circuited) .  It  is 
found,  however,  that  this  method  is  not  as  efficient  as  that  shown  in  the 
figure. 


150 


MANUAL    OF    RADIO    TELKGRAPHY    AND   TELEPHONY. 


Both  foiulcnsors,  CCj  and  CCo,  are  on  the  same  shaft,  and  hence  are 
simultaneously  adjusted. 

As  shown,  the  usual  detector  circuit  is  used,  the  telephones  being  placed 
around  the  stopping  condenser. 

By  a  simple  switching  arrangement,  the  detector  system  can  be  directly 
attached  to  the  primary  circuit.  This  is  used  for  a  "  stand-by  "  or  "  pick- 
up "  circuit.  Only  one  circuit  has  to  be  tuned  in  this  case.  Whereas,  with 
all  other  pick-up  circuits  heretofore  used,  the  broadness  of  tuning  was  too 
great  to  enable  the  circuit  to  be  of  any  great  use  (as  so  much  interference 
was  received  that  it  was  impossible  to  pick  out  the  signal  desired),  the 
circuit  shown  here  is  quite  selective,  and  hence  is  not  disturbed  to  so  great 
an  extent. 


CCi  BC 


S^ 


CCo 


Fig.  92b. — Receiver  Circuit. 


Fig.  92c. — Pick-up  Circuit. 


An  ideal  pick-up  circuit,  it  is  true,  is  one  that  picks  up  any  signal, 
regardless  of  wave  length,  but  this  would  work  only  when  the  number  of 
stations  sending  within  range  was  very  limited,  and  atmospheric  distur- 
bances were  at  a  minimum,  on  the  other  hand,  a  pick-up  circuit  that  is 
strongly  selective  defeats  the  very  purpose  that  its  name  implies.  The 
circuit  shown  is  a  mean  between  those  two  extremes,  and  is  rather  broadly 
hined.  It  is  very  easy,  with  this  circuit,  to  tell  if  any  one  is  sending  within 
the  range  of  a  wave  length  for  which  the  receiver  was  designed,  as  a  con- 
tinuous variation  of  the  one-tuned  circuit  concerned  can  be  made  over  the 
entire  range  in  a  very  short  time.  Under  many  conditions,  this  "  pick-up  " 
circuit  can  be  used  for  regular  work,  shifting  to  the  two-circuit  system 
when  interference  develops. 

In  this  form  of  circuit,  the  coupling  condenser  is  again  :ised  in  its  func- 
tion of  controlling  the  energy  transferred  to  the  detector.    In  general,  this 


MANUAL    OF    RADIO    TELEGRAPHY   AND   TELEPHONY.  151 

condenser  sliould  be  set  at  or  near  its  maximum  when  "  picking-up  "  is 
being  done. 

The  coupling  would  prevent  the  rectified  currents  from  the  detector 
from  passing  through  the  inductance  L^  and  thence  through  the  telephones 
if  the  telephones  were  placed  around  the  stopping  condenser,  as  they  are 
in  the  two-circuit  system  of  sheet  13.  This  is  obviated  by  placing  the 
telephones  around  the  detector  in  the  pick-up  circuit.  This  results  in  a 
slight  decrease  of  efficiency. 

General  Description. — Fig.  92e  shows  the  front  of  box  containing  the  set. 
Referring  to  the  numbers  on  fig.  92e  the  function  of  the  various  parts  is 
as  follows :  Knob  A-7  controls  the  series  condensers  8,  9  and  10  and  load- 
ing coils  36.  When  on  the  first  point  the  smallest  series  condenser  is  in 
antenna  circuit,  on  second  point  the  next  condenser,  etc. ;  on  the  fourth 
point  neither  condensers  nor  loading  coils  are  connected ;  on  the  fifth  point 
the  smallest  loading  coil  is  in  antenna  circuit  and  so  on  to  ninth  point 
where  loading  coil  of  largest  inductance  is  put  in  the  circuit.  This  knob 
also  controls  through  a  system  of  gears  and  levers,  pointer  A-4  so  that  as 
A-7  goes  from  first  to  ninth  point  the  pointer  A-4  moves  from  outer  circle 
on  dial  A-5  into  inner  circle. 

Dial  A-5  is  graduated  in  wave  length  similarly  to  dial  A-26  using  con- 
ventional lettering  for  standard  wave  length. 

Knob  A-6  controls  large  inductance  45  to  46  and  dial  A-5  rotates  with  it. 

Knob  A-8  controls  small  inductance  51-52  and  is  connected  to  pointer 
A-4  in  such  a  way  that  it  can  swing  the  pointer  through  a  small  arc. 

In  this  way  the  dial  A-5  after  once  being  graduated  for  the  particular 
antenna  in  use  will  indicate  the  wave  length  of  antenna  circuit  directly. 
The  same  wave  length  will  appear  on  several  circles  of  dial  A-5.  In  general 
for  sharpest  tuning  the  inner  circle  is  used  and  for  loudest  signal  the  outer 
circle  on  which  the  desired  wave  length  can  be  found. 

Knob  A-9  controls  the  two  coupling  condensers  CCi  at  13-14  and  CCj 
at  32-33. 

Knob  A-10  controls  stopping  condenser  BC  at  54-55. 

Knob  A-20  is  switch  at  60,  76.  In  position  marked  Sec,  the  switch 
shown  on  fig.  92a  gives  connection  as  shown  in  fig.  92b.  In  position 
marked  Pri.  the  connections  are  as  shown  in  fig.  92c  for  pick-up  circuit. 

Knob  A-27  controls  secondary  condenser  C,  at  25-26  and  A-28  controls 
secondary  inductance  L,  at  16. 

Dial  A-26  indicates  wave  length  of  secondary. 

Knob  A-21  controls  potentiometer  61-75. 

A-11  and  13  are  connections  to  antenna  and  ground  with  safety  spark 
gap  between  them. 

A-16  and  17  are  connections  for  detector  battery. 

A-18  and  19  are  switches  in  detector  and  buzzer  circuits. 

A-22  is  the  buzzer. 

A-32  and  33  are  telephone  and  AA-34  and  35  are  detector  connections. 


152 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


A-1-3  and  A-29-31  provide  places  in  which  extra  inductances  or 
capacities  may  be  connected  in  primary  or  secondary  circuits  respectively. 

To  use  type  A  receiver  for  receiving  undamped  waves  with  the  oscillating 
Audion,  the  telephone  binding  posts  of  the  receiver  are  short  circuited  and 
the  crystal  detector  removed.  The  detector  binding  posts  are  then  con- 
nected to  the  Eo  and  Eg  terminals  of  the  Audion  box  (fig.  92d) .  This  box 
contains  the  grid  condenser  GC,  the  bridging  condenser  C3  and  the  battery 
of  dry  cells  B,  of  36  volts,  and  has  terminals  for  attaching  the  telephones 


BAT.  "B" 


iRc. 


^ft£_ 


A-'' 


RECEIVING   SET 


^^im% 


'LA 


u- 


I.I 


BAT.  "A" 

Fig.  92d. — Diagram  of  Connections  Type  A  Receiver,  for  Receiving  Undamped 
Waves  with  the  Oscillating  Audion. 

and  the  wires  from  the  plate  (red),  and  grid  (green),  of  the  bulb.  A 
storage  battery  of  six  volts  for  heating  the  filament  in  the  bulb  is  then  con- 
nected to  the  terminals  A-\-A,  taking  care  that  the  filament  rheostat  is 
placed  in  the  position  "  in  "  before  the  current  is  turned  on  at  the  "  on  " 
and  "  off  "  switch.  The  rheostat  is  then  adjusted  so  that  the  filament,  if 
of  the  Hudson  type,  burns  with  about  the  brightness  of  the  filament  of  a 
carbon  incandescent  lamp.  The  brightness  should  not  exceed  a  dull  red  if 
the  filament  is  coated  with  oxide. 

The  grid  condenser  and  the  stopping  condenser  are  set  about  one-fourth 
in,  and  the  tuning  condenser  C2  set  at  zero,  then  if  the  Audion  is  to  be  used 
in  ultra- Audion  connection  the  Audion  switch  is  set  "  arc  "  and  the  B 
battery  potentiometer  adjusted  until  oscillations  are  produced.    This  con- 


MANUAL   OF    RADIO   TELEGRAPHY    AND   TELEPHONY. 


153 


y  Receiving  Set,  Type  A. 


154 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


ditioii  may  be  tested  by  touching  with  the  moistened  finger  a  bare  portion 
of  the  wire  connecting  the  receiver  with  Ha.  If  oscillations  are  present, 
touching  the  wire  will  produce  a  clicking  or  rustling  noise  in  the  tele- 
phones. The  secondary  condenser  is  next  increased  to  give  the  required 
wave  length  and  the  Audion  again  tested  for  oscillations  by  touching  the 
wire  at  Ea. 

If  the  set  is  provided  with  tickler  or  back-coupling  coils  the  Audion 
switch  is  placed  on  "  spark."  The  coil  T2  of  from  2  to  6  M.  H,  is  con- 
nected to  the  Ijinding  posts  marked  "  tickler/'  and  T^,  of  0.5  to  3  M.  H. 
connected  to  the  outside  secondary  loading  coil  terminals,  and  the  coupling 
T^Tg  adjusted.  If  oscillations  are  not  produced  the  terminals  of  T^  should 
be  reversed.  The  back-coupling  connection  usually  gives  more  stable  oscil- 
lations than  the  ultra-Audion  connection.  Considerable  amplification  of 
spark  signals  without  the  loss  of  musical  note  may  be  obtained  by  closing 
the  back  coupling  to  a  point  not  quite  close  enough  to  produce  oscillations. 

VARIABLE  CONDENSERS. 

In  fig.  92f  is  shown  the  type  of  variable  condenser  used  in  radio  receiving 
circuits  and  wave  meters.  It  consists  essentially  of  two  sets  of  semicircular 
plates  one  fixed  and  the  other  capable  of  being  rotated  so  that  its  plates  may 


Fig.  92f. — Variable  Condenser. 


occupy  positions  between  the  plates  of  the  fixed  set.  The  capacity  is  varied 
by  the  relative  position  of  the  semicircular  plates.  The  condenser  shown 
is  manufactured  by  the  De  Forest  Eadio  Telephone  and  Telegraph  Co.  for 
general  radio  work. 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPTTONY.  155 

CONDENSERS  IN  RECEIVING  CIRCUITS. 

203.  A  variable  receiving  condenser  usually  consists  of  semi-circular 
metal  plates  separated  by  air  dielectric,  alternate  plates  being  fixed.  The 
other  plates  are  movable  on  an  axis,  by  turning  which,  any  desired  amount 
of  the  movable  plates  can  be  included  between  the  fixed  plates.  The  axis 
carries  a  pointer  which  moves  over  a  scale  graduated  in  degrees  or 
directly  in  microfarads.  If  used  in  connection  with  a  fixed  inductance, 
the  scale,  like  a  wave  meter,  which  in  this  case  it  becomes,  may  be  grad- 
uated directly  in  wave  lengths.  Some  of  the  Stone  receiving  sets  had 
sliding  glass  plate  condensers,  and  the  Pierce  sets,  step-by-step  variable 
condensers  in  the  receiving  circuits,  but  the  revolving  plate  type  described 
above  is  practically  a  standard  and  is  illustrated  in  fig.  109. 

Variable  condensers  now  supplied  have  the  limits  of  their  capacity 
marked  on  the  name  plate  in  microfarads. 

Fixed  condensers,  in  receiving  circuits,  are  often  called  stopping  con- 
densers (art.  196).  They  may  be  of  any  compact  type,  and  (except  in 
the  case  of  a  fixed  condenser  for  use  with  the  ticker  detector,  which  should 
have  a  comparatively  large  capacity),  the  capacity  may  be  quite  small. 

INDUCTANCES   IN   RECEIVING   CIRCUITS. 

204.  Variable  inductances  include  the  step-by-step,  roller,  and  vari- 
ometer types.  The  first  is  made  up  of  plug  or  dial  steps,  giving  a  limited 
number  of  changes,  one  section  of  a  coil  being  varied  at  a  time,  or  it  may 
be  a  cylindrical  coil  of  insulated  wire  wound  on  hard  rubber,  glass,  or  por- 
celain, one  point  in  each  turn  being  bare  and  co^nnections  being  made  by 
a  slider  giving  as  many  adjustments  as  there  are  turns  of  wire  in  the 
coil. 

In  the  DeForest  pancaTce  tuners  the  coil  was  a  flat  spiral  of  insulated 
wire  on  glass,  one  point  in  each  turn  being  bared  so  as  to  form  an  arc  of 
a  circle,  the  end  of  an  arm  pivoted  at  the  center  of  this  circle  making 
contact  at  any  desired  point. 

Shoemaker  sets  (fig.  82)  have  a  single  roller  inductance,  the  bare  wire 
being  wound  in  a  spiral  groove  on  an  ebonite  cylinder.    A  sliding  contact, 
on  a  rod  parallel  to  the  cylinder,  works  in  the  groove  and  is  pressed 
against  the  wire  by  a  spring.    By  revolving  the  cylinder  an  infinite  num 
ber  of  adjustments  can  be  obtained. 

Earlier  Fessenden  sets  (figs.  79  and  82),  have  double  roller  inductances, 
by  turning  which,  the  wire  can  be  reeled  from  one  roller  to  another  as 
desired.  On  one  roller  the  turns  are  insulated  from  each  other  and  on 
the  other  they  are  short  circuited  so  that  any  desired  length  can  be  re- 
tained in  the  circuit. 

None  of  the  above  types  of  variable  inductances  can  be  readily  mounted 
so  as  to  vary  the  mutual  induction  between  them  by  any  definite  amount. 
They  are  suitable  for  loading  but  not  suitable  for  loose  coupling. 


156  MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 

For  this  reason  the  preferred  types  of  receiving  circuits  are  made  up  of 
fixed  inductances  (or  those  varied  by  plug  or  dial  steps),  mounted  so  that 
they  can  either  be  pulled  apart  or  one  coil  revolved  so  as  to  change  its  plane 
and  hence  the  mutual  induction  with  reference  to  the  other  or  others. 
The  variometer  type,  mounted  like  variable  condensers,  are  now  being 
manufactured.  Their  self-induction  can  be  varied  quickly  and  con- 
veniently and  close  adjustment  of  period  (tuning)  made  with  them  or 
with  the  variable  condensers,  but  the  entire  coil  is  always  in  circuit. 

Each  section  of  an  inductance  not  in  circuit  should  be  opened  at  both 
ends,  i.  e.,  entirely  disconnected,  and  if  its  natural  period  is  large  it  should 
be  mounted  so  that  the  inductive  effect  of  active  parts  on  it  is  a  minimum. 
This  applies  especially  to  loading  coils  for  long  wave  lengths.     (Fig.  92.) 

All  inductances  are  wound  on  hard  rubber,  porcelain  or  glass  and  so  as  to 
have  a  minimum  high  frequency  resistance.  The  decrement  of  the  entire 
circuit  must  not  exceed  .3. 

From  the  formula  for  damping  d  —  it  can  readily  be  seen  that  a 

very  pronounced  natural  period — a  stiff  circuit — can  not  be  obtained 
unless  the  self-induction  is  large  compared  with  the  total  resistance  (in- 
cluding the  radiation  resistance) . 

DETECTORS. 

205.  There  are  two  types  of  detectors  now  in  general  use,  viz.,  the 
Audion,  and  the  Crystal  or  rectifying  detector.  The  electrolytic  is  used 
only  as  a  standard  for  comparison.  Coherers  and  microphones  are  prac- 
tically obsolete,  and  comparatively  few  of  the  magnetic  detectors  have 
been  installed,  but  the  use  of  audions  and  ultra-audions  is  increasing. 
Unlike  coherer  detectors,  all  types  of  crystal,  magnetic,  electrolytic  and 
audion  detectors  are  self-restoring.  Generally  speaking  all  should  be 
put  on  open  circuit  while  sending,  to  preserve  them  from  injury  due  to 
induced  potentials  and  currents. 

The  ordinary  detector  serves  as  well  for  receiving  the  continuous 
modified  oscillations  of  wireless  telephony  as  for  the  groups  of  oscillations 
in  ordinary  wireless  telegraphy. 

THE  ELECTROLYTIC  DETECTOR.  ^ 

206.  It  consists  of  a  fine  platinum  wire  just  touching  an  electrolyte 
made  either  of  a  20^  solution  of  nitric  or  sulphuric  acid  or  an  alkali. 
Of  these  the  nitric  acid  solution  is  preferred.  The  other  electrode  is  also 
of  platinum.  The  containing  cup  (fig.  79)  is  made  quite  small  so  that 
the  cohesive  power  of  the  electrolyte  will  prevent  splashing  in  a  sea  way. 
The  electrolytic  detector  must  have  the  fine  wire  terminal  connected  to 
the  positive  pole  of  the  local  battery  (fig.  79),  otherwise  the  device  is 
not  operative. 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TKLEPHONY.  157 

Dr.  Austin  states  that  the  higher  the  frequency,  the  finer  the  wire 
should  be,  and  that  the  depth  of  immersion  does  not  matter  if  the 
detector  is  not  directly  in  series  in  the  closed  circuit. 

When  a  current  flows  through  the  electrolyte,  the  latter  is  decomposed 
(the  action  being  called  electrolysis)  liberating  oxygen  at  the  anode  and 
hydrogen  at  the  cathode.  The  accumulation  of  these  non-conducting 
gases  on  the  electrodes  interferes  with  the  passage  of  the  current,  which 
soon  ceases  to  flow  and  the  cell  is  then  said  to  be  polarized. 

The  fine  wire  anode  is  then  insulated  by  the  oxygen,  which  forms  the 
dielectric  of  a  small  condenser,  of  which  one  conducting  surface  is  the 
electrolyte  and  the  other  the  wire  point. 

The  critical  potential  of  the  detector  is  just  below  that  necessary  to 
break  down  this  insulating  layer  of  oxygen  and  is  determined  by  increas- 
ing the  potential  at  the  detector  terminals  by  means  of  the  potenti- 
ometer until  a  bubbling  or  hissing  sound  is  heard  in  the  receiving 
telephone ;  then  resistance  is  cut  in  until  this  sound  just  ceases. 

When  electric  oscillations  are  impressed  on  this  condenser,  the  polariza- 
tion layer  breaks  down  and  permits  a  pulse  of  direct  current  from  the 
battery  to  pass  through  the  cell  and  telephone.  As  soon  as  the  oscilla- 
tions cease  the  polarization  is  restored. 

Except  when  they  are  very  strong,  the  loudness  of  the  sounds  produced 
in  the  telephone  is  an  exact  measure  of  the  energy  of  the  oscillations 
passing  through  the  cell. 

This  constancy  of  action  of  the  electrolytic  cell  is  utilized  as  a  means 
of  comparing  the  sensitiveness  of  detectors,  the  standard  being  the  sen- 
sitiveness of  an  unjacketed  platinum  wire  electrode  .0002  in  diameter  in 
a  solution  of  20%  nitric  acid.* 

Glass  jacketed  electrodes  formed  by  sealing  the  wire  in  glass  (the  two 
having  the  same  coefficient  of  heat  expansion)  have  been  used,  but  are 
less  reliable  and  in  general  less  sensitive  and  are  no  longer  supplied. 
Some  of  these  glass  points  were  made  hook  shaped,  the  hook  pointing 
upward  to  facilitate  depolarizing  but  no  increase  in  sensitiveness  waa 
noted  on  this  account. 

With  the  Shoemaker  receiving  sets  was  furnished  what  was  called  a 
primary  cell  detector.  The  electrolyte  used  was  a  20^  solution  of  sul- 
phuric acid  and  the  other  electrode  was  a  zinc  rod  amalgamated  with 
mercury,  which  in  the  acid  solution  gave  a  difference  of  about  .7  volt 
between  zinc  and  platinum.  No  local  battery  was  required  (fig.  82).  At 
times  this  detector  compared  favorably  with  the  one  just  described,  but 
was  in  general  more  irregular  and  less  sensitive  in  its  action. 

♦  Dr.  Austin  has  invented  a  "  detector  tester  "  which  affords  a  means  of 
direct  comparison  between  detectors  operating  under  the  same  conditions. 


158  MANUAL    OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 

In  all  electrolytic  detectors  very  strong  signals  or  static  discharges 
produce  actual  sparking  or  an  explosive  action  in  the  electrolyte,  which 
destroys  the  platinum  point  and  an  operator  must  be  constantly  on  the 
lookout  to  protect  his  point  from  burning  out.  The  best  results  in 
electrolytic  detectors  have  been  obtained  with  a  distance  between  electrodes 
of  approximately  \  inch. 

RECTIFYING  DETECTORS. 

207.  There  are  certain  substances  which  when  brought  together  in  not 
too  close  contact,  have  the  property  of  producing  a  direct  current  when  an 
alternating  current  or  electrical  oscillations  are  sent  through  them.  The 
cause  of  this  action  is  not  yet  known.  Among  these  substances  are  car- 
bon in  contact  with  steel,  tellurium  with  aluminum  or  galena,  silicon 
with  any  of  the  ordinary  metals,  and  certain  crystals. 

The  first  of  the  crystal  detectors  to  be  supplied  was  General  Dun- 
woody's  carborundum  crystal  detector. 

Since  rectifying  detectors  permit  the  passage  of  current  in  but  one 
direction,  they  produce  pulses  of  direct  current.  These  pulses,  if  strong 
enough,  can  be  heard  in  a  telephone  so  that  local  batteries  are  not  re- 
quired, although  a  slight  increase  of  sensitiveness  is  noted  in  some  de- 
tectors with  an  E.  M.  F.  across  the  terminals  of  the  detector  of  about  0.2 
volt. 

Rectifying  detectors  are  connected  in  receiving  circuits  in  the  same 
manner  as  the  electrolytic. 

Their  sensitiveness  for  general  use  is  practically  equal  to  the  electro- 
lytic and  their  simplicity  makes  them  the  more  suitable.  They  are  in 
general  less  sensitive  to  injury  from  static  discharges,  strong  signals,  or 
induced  currents  from  sending,  than  the  electrolytic,  but,  like  coherers, 
different  crystals  of  the  same  material  vary  widely  in  sensitiveness  and 
sensitive  spots  in  any  crystal  have  to  be  found  by  trial  and  when  found 
are  not  constant.  They  are  thus  not  as  capable  of  quick  readjustment 
as  the  electrolytic,  but  their  other  advantages  are  such  as  to  be  con- 
clusive as  regards  their  use. 

The  carborundum  detector  when  first  introduced  was  simply  held 
between  two  points  or  wrapped  with  copper  wire  for  one  connection,  with 
a  needle,  knife  edge,  or  more  blunt  piece  of  metal  for  the  other.  It  was 
later  found  that  embedding  a  large  part  of  the  crystal  in  a  conductor 
such  as  solder  or  a  mercury  paste,  and  thus  limiting  the  rectification  to 
one  contact  only,  produced  much  better  results  and  carborundum  crystals 
have  been  found  equal  in  sensitiveness  to  other  crystals  now  generally 
utilized. 

Pickard's  silicon  detector  followed  the  carborundum  and  is  still  in 
use  but  it  has  been  largely  superseded  by  the  Perikon  &  Pyron,  supplied 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY.  159 

with  the  receiving  set  illustrated  in  fig.  86.  The  Perikon  detector  con- 
sists of  two  crystals,  chalcopyrites  and  zincite.  A  number  of  zincite 
crystals  are  held  in  a  conducting  disc,  a  crystal  of  chalcopyrites  is 
mounted  so  that  it  can  be  brought  into  contact  with  any  part  of  any  of 
the  zincite  crystals  at  will,  and  the  pressure  between  the  two  regulated. 
In  the  adjustment  for  maximum  intensity  of  signals,  the  exact  degree  of 
pressure  and  the  most  favorable  points  of  contact  are  of  importance. 
These  can  only  be  ascertained  by  trial  and  test  with  the  testing  buzzer. 

The  sensitiveness  of  the  Perikon  may  be  approximately  doubled  by 
connecting  a  battery  across  its  terminals  so  as  to  give  approximately  0.2 
volt.    The  positive  pole  must  be  connected  to  the  single  crystal. 

The  Pyron  consists  of  a  crystal  of  iron  pyrites  in  contact  with  a 
metal  point  like  the  silicon.  This  is  very  satisfactory  for  strong  signals 
and  constant  in  its  action.  The  iron  pyrites  is  more  sensitive  when  the 
pressure  of  the  metal  point  is  adjustable.  The  area  of  contact  is  also  a 
determining  factor  of  sensitiveness;  comparatively  fine  points  will  dis- 
cover sensitive  places  on  irregular  crystals,  which  blunt  points  will  not. 

The  Perikon  is  more  sensitive  and  must  be  protected  against  strong 
signals.  The  zincite  is  the  crystal  injured  by  strong  signals.  It  should 
not  be  subjected  to  heavy  pressures  or  grinding  from  the  chalcopyrite. 
When  deadened  the  zincite  crystals  can  be  made  operative  by  scrubbing 
them  with  a  bristle  brush  wet  with  carbon  bisulphide,  then  with  soap  and 
water  and  then  rinsing  with  fresh  water  and  drying.  In  damp  weather 
or  in  tropical  climates  this  detector  is  improved  by  spreading  a  drop  of 
paraffin  oil  over  the  surface  of  the  crystals.  This  comment  applies  to  the 
silicon  also. 

Galena,  cerusite  (a  form  of  galena)  and  iron  pyrites  are  all  giving  satis- 
factory use  by  mounting  so  as  to  have  contact  all  over  one  surface  and  a 
very  fine,  flexible  wire  point,  just  touching  the  other  surface. 

I 

VACUUM  TUBE  DETECTORS. 

208.  The  two  forms  which  have  been  used  are  kno\vn  as  the  valve  and 
the  audion,  illustrated  in  figs.  84  and  88.  The  valve  was  discovered  by 
Fleming,  and  is  sometimes  called  the  Fleming  valve.  It  is  a  rectifier, 
permitting  the  passage  of  current  in  one  direction  only.  It  consists  of  a 
special  incandescent  lamp  (see  fig.  8-i),  operated  by  a  12-volt  storage  bat- 
tery and  having  a  small  sheet  or  cylinder  oE  metal  held  in  the  bulb  near  the 
filament.  Lamp  filaments  when  glowing  emit  negative  electricity,  which 
carries  away  part  of  the  filament  and  causes  the  darkening  of  the  bulb 
seen  on  old  carbon  lamps.  The  vacuum  thus  becomes  a  conductor  in  one 
direction  only.    It  is  not  found  to  be  a  very  sensitive  one. 


160 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


The  audion  (fig.  88)  has  a  metal  grid  interposed  between  the  metaJ 
plate  and  the  lamp  filament.  In  the  valve,  the  metal  plate  is  connected 
to  the  receiving  circuit,  but  in  the  audion,  the  grid  is  connected  to  the 
receiving  circuit,  while  the  plate  is  connected  to  the  telephone.  In  the 
valve,  the  variations  of  current  in  the  receiving  circuit  produce  differences 
of  potential  between  the  filament  and  the  plate.  In  the  audion,  these 
differences  of  potential  are  between  the  filament  and  the  grid ;  or,  as  it  is 
perhaps  better  to  say,  the  grid  is  charged  by  the  received  oscillating  cur- 
rents. In  addition  to  this  difference,  the  audion  has  a  local  battery  with 
its  positive  pole  connected  to  the  metal  plate,  and  its  negative  pole  to 
the  lamp  filament.  This  battery,  as  well  as  the  battery  supplying  the 
lamp,  has  a  variable  voltage.  The  battery  voltage  and  lamp  voltage  must 
both  be  adjusted  to  secure  the  greatest  sensitiveness  of  this  detector ;  but 


Fig.  88a. — Amplifying  Audion. 


this  adjustment  is  permanent  for  any  given  conditions.  The  charge  on 
the  grid,  produced  by  the  incoming  signals,  interferes  with  the  flow  of 
negative  electricity  between  the  filament  and  the  plate.  This  flow  of 
negative  electricity,  when  the  heat  from  the  filament  and  the  local  battery 
voltage  are  properly  adjusted,  produces  a  current  through  t]ie  audion  of 
the  order  of  a  milliampere.  This  current  flows  through  the  receiving 
telephone  and  variations  in  it,  produced  by  the  varying  charge  on  the 
grid,  are  what  make  the  signals  heard  in  the  telephone. 

The  audion  has  the  further  advantage  over  the  valve,  in  that  the  tele- 
phone can  be  replaced  by  the  primary  of  a  transformer,  the  secondary  of 
which  is  connected  to  another  audion,  with  the  result  of  amplifying  the 
signals  produced.  (See  fig.  88a.)  Audion  bulbs  have  tantalum  lamp 
filaments,  and  plate  and  grid  are  usually  double,  one  on  each  side  of  the 
filament.  The  plate  and  grid  are  of  nickel.  The  audion  can  also  be  used 
as  a  heterodyne  (art.  201).  When  connected  for  receiving  continuous 
oscillations  it  is  called  "  the  ultra-audion." 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


161 


We  see,  therefore,  that  the  audion  is  suitable  for  use  with  arc,  as  well 
as  spark  sets,  and  also  as  an  amplifier;  thus  combining  within  itself  the 
qualities  of  all  other  detectors. 

THE  OSCILLATING  AUDION. 

If  a  low  resistance  circuit,  consisting  of  a  coil  and  condenser,  be  con- 
nected to  an  audion,  a  lead  from  one  side  of  the  condenser  connecting 
through  a  stopping  condenser  to  the  grid,  and  a  lead  from  the  other  end 
of  the  condenser  to  the  plate,  it  is  found  that  the  audion  produces  oscilla- 
tions in  the  circuit,  these  oscillations  being  determined  as  to  frequency  by 


Fig.  92g. — DeForest  Audion-Detector. 


the  inductance  and  capacity  of  the  associated  circuit.  This  form  of 
audion  connection  has  been  termed  by  Dr.  DeForest  the  "  TJltraudion." 
It  was  later  found  that  oscillations  could  similarly  be  developed  with  the 
condenser  connected  to  the  grid  (through  stopping  condenser)  and  the  fila- 
ment respectively,  by  inserting  an  inductance  in  the  B  battery  circuit  lead- 
ing to  the  plate,  and  coupling  this  coil  with  the  correct  polarity  to  the  in- 
ductance of  the  oscillating  circuit.  This  coil  has  been  variously  termed 
the  "  back-coupling  coil,"  the  "  feed-back  coil,"  and  "  tickler  coil." 

This  form  of  oscillating  audion  is  now  generally  used  for  receiving, 
using  the  method  of  beats.  The  secondary  circuit  of  the  radio  receiver  is 
connected  as  above  to  the  ultraudion,  and  oscillations  are  set  up.  The 
frequency  of  these  oscillations  is  made  slightly  different  from  the  frequency 
of  the  incoming  signals,  and  the  two  slightly  differing  frequencies  combine 
11 


162  MANUAL   OF   RADIO   TELEGRAPHY   AND   TELEPHONY. 

to  form  a  third  which  is  within  the  range  of  audibility.  If  the  frequencies 
differ  by  1000,  for  instance,  the  resultant  frequency  gives  a  note  in  the 
receiving  telephone  the  same  as  from  a  500-cycle  spark  set.  This  note  is  of 
course  under  the  operator's  control,  as  by  varying  the  secondary  condenser 
of  the  receiver  the  frequency  of  the  oscillations  generated  by  the  ultraudion 
may  be  varied,  and  hence  the  difference  in  the  two  frequencies  may  be  made 
greater  or  less  than  1000. 

Larger  size  tubes  are  now  in  general  use  as  transmitting  devices,  the 
general  principle  of  generation  of  oscillations  being  as  explained  above. 
The  transmitting  units  are  sometimes  known  as  "  Oscillions." 


MAGNETIC   DETECTORS. 

209.  The  operation  of  magnetic  detectors  depends  on  the  fact  that 
when  iron  is  being  magnetized  its  magnetization  is  somewhat  delayed  in 
time  behind  the  impressed  magnetizing  force,  and  when  in  this  condition 
the  iron  is  very  sensitive  to  any  change  in  the  magnetizing  force,  a 
very  small  increase  of  which  will  produce  a  momentarily  large  increase 
in  the  strength  of  the  magnetic  field. 

Many  patents  have  been  issued  for  various  forms  of  magnetic  detectors, 
the  best  known  and  the  most  largely  used  of  which  is  Marconi's,  patented 
in  England  in  1902.  It  is  not  injured  by  strong  sending,  but  is  not  as 
efficient  as  the  crystal  detector,  the  electrolytic  nor  the  audion. 

In  its  present  form  it  consists  of  a  flexible  band  of  silk-covered  iron 
wires,  moved  by  clockwork  around  two  pulleys  which  support  it.  A  glass 
tube,  through  which  the  band  passes,  has  a  primary  winding  of  insulated 
wire  in  series  with  the  aerial  and  a  secondary  winding  forming  a  closed 
circuit  through  a  telephone.  Close  to  the  secondary  windings  are  placed 
similar  poles  of  two  horse-shoe  magnets,  which  magnetize  the  iron  band 
slowly  moving  under  them.  Electric' oscillations  in  the  primary  winding, 
produced  by  passing  electric  waves,  produce  momentary  changes  in  the 
magnetization  of  the  iron  band  under  the  magnets,  and  these  changes 
induce  oscillating  currents  in  the  secondary  winding  which  produce 
sounds  in  the  telephone. 

An  elementary  diagram  of  this  magnetic  detector  is  shown  in  fig.  87. 
It  requires  no  local  battery,  and,  not  being  subject  to  burn-outs  except 
from  very  large  currents,  it  is  a  very  convenient  instrument,  but  is  not 
as  sensitive  as  those  previously  described,  especially  for  short  wave 
lengths.  There  are  other  methods  of  connecting  this  detector  than  that 
shown  in  fig.  87,  but  since  comparatively  few  magnetic  detectors  are  in 
use  they  are  not  shown  here. 


MANUAL   OF   RADIO   TELEGRAPHY   AND   TELEPHONY. 


163 


SLIPPING  CONTACT  DETECTOR. 

210.  In  its  present  form  this  consists  of  a  small  bundle  of  fine  wires,  or 
a  single  wire  resting  lightly  on  the  rim  of  a  wheel  of  conducting  material, 
which  is  revolved  at  high  speed  by  a  small  motor.  It  is  not,  in  general,  as 
satisfactory  as  crystal  detectors,  but  is  suitable  for  receiving  undamped 
oscillations  (fig.  89).  Its  note  is  too  low  to  permit  good  results  in 
receiving,  when  there  is  any  static. 

COHERERS  AND  LODGE-MUIRHEAD  DETECTOR. 

211.  Coherers  being  practically  obsolete  are  i»ot  described.  They  are 
illustrated  in  fig.  93. 

Of  the  many  other  kinds  of  detectors  that  have  been  used,  the  Lodge- 
Muirhead,  which  would  work  either  with  a  telephone  or  recorder,  was  the 
most  sensitive  and  reliable. 


SLABY   ARCO   COHERER 


FiQ.  93. 


r~~i 


|_      .  -!^-~V 

c 

c 
c 

4 

) 
) 
) 

s 

LODGE-MUIRHEAD 
COHERER 


Fig.  93a. 


It  is  illustrated  in  fig,  93a,  and  consists  of  a  polished  steel  disc  rotated 
by  clockwork,  its  edge  just  touching  the  edge  of  a  globule  of  mercury 
covered  by  a  film  of  oil.  A  pad  which  rubs  against  the  disc  keeps  it  clean 
and  bright.  This  coherer  may  be  direct  or  inductively  connected  in  or 
to  the  aerial.  Its  conductivity  changes  sufficiently  to  relay  a  current  for 
working  a  siphon  recorder  so  that  it  is  suitable  for  use  in  connection  with 
determining  longitudes  by  wireless  telegraphy. 

It  is  also  self-restoring  and  can  therefore  be  used  with  a  telephone. 


164 


MANUA]>    OF    IJAUIO    TELKGRAPHY   AND   TELEPHONY. 


TESTING   BUZZERS. 


212.  A  testing  buzzer  with  its  battery  of  one  cell,  its  condenser  and 
circuit,  is  a  miniature  sending  set  and  an  important  auxiliary  of  every 
receiving  set.  The  oscillations  set  up  in  its  circuit  induce  currents  in 
the  receiving  circuits,  which  serve  by  their  effect  to  determine  the  sensi- 


FiG.  94. — Wireless  Telegraph  Test  Buzzer.     For  Ships. 


Hi 


y. 


Pl^TlNUM  CONTACra, 


[    BUZZER 


Fig.  95. 


tiveness  and  readiness  for  operation  of  the  detector.  A  testing  buzzer 
outfit  furnished  with  the  Telefunken  sets  is  shown  in  fig.  94,  the  con- 
nections of  that  supplied  with  the  l-P-76  receiving  sets  in  fig.  95.  Tuned 
buzzer  circuits  are  useful  in  measurements. 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY.  165 

RECEIVING   TELEPHONES. 

213.  The  low  resistance  telephones  in  ordinary  use  are  not  suitable 
for  wireless  work  on  account  of  the  high  resistance  of  the  detectors,  which 
may  be  several  thousand  ohms.  Specially  made  telephones  are  required 
to  produce  the  best  effect.  The  magnet  wire  has  very  thin  silk  or 
enamel  insulation.  A  length  of  wire  whose  resistance  is  approximately 
equal  to  that  of  the  detector  can  be  efficiently  used.  This  is  from  1000 
to  2500  ohms  in  each  of  the  double  head  telephones  supplied. 

For  low  frequencies,  telephones  with  adjustable  diaphragms  or  magnets 
are  found  to  be  about  ten  times  as  sensitive  as  the  ordinary  type  with  a 
fixed  distance  between  diaphragms  and  magnets. 

This  advantage  decreases  as  the  frequency  approaches  the  present 
standard  of  500  cycles  (1000  sets  of  sparks  per  second),  but  is  still 
sufficient  to  warrant  the  retention  of  the  adjustable  diaphragm  type. 

An  improvement  recently  made,  is  the  substitution  of  a  single  magnet, 
located  under  the  center  of  the  diaphragm,  for  the  pair  of  magnets  in  the 
usual  construction.  Also,  what  are  known  as  "  reed  "  telephones  are  an 
improvement  on  the  usual  double  magnet  type. 

At  stations  where  it  is  necessary  to  listen  on  two  wave  lengths  at  the 
same  time,  one  half  of  the  head  set  may  be  connected  to  one  receiving  set 
and  the  other  half  to  the  other  receiving  set.  Attempts  are  being  made 
to  apply  the  principles  of  "  tune  shifters  "  to  receiving  sets  also,  so  that 
an  operator,  by  turning  one  wheel,  can  shift  through  his  entire  range, 
keeping  both  circuits  in  tune  and  maintaining  proper  coupling  through- 
out; this  wheel  to  be  graduated  in  wave  lengths.     (Art.  170.) 

In  some  Marconi  sets  low  resistance  receiving  telephones  are  used, 
connected  through  a  step-down  transformer.     (See  fig.  84.) 

Batteries  and  potentiometers  are  used  with  receiving  telephones,  theii 
connections  being  as  shown  in  figs.  77  to  89. 

In  order  to  produce  sound,  intermittent  work  must  be  done  on  a  tele- 
phone diaphragm  at  a  certain  minimum  rate.  (See  arts.  154  and  155.) 
In  other  words  we  must  apply  a  certain  power  to  it — power  being  rate  oi 
doing  work.  The  frequency  must  be  within  the  limits  of  audibility. 
(Art.  183.) 

It  appears  that  with  crystal  detectors  we  obtain  this  power  directly 
from  the  aerial,  while  with  the  electrolytic,  and  audion  the  power  from  the 
aerial  only  works  the  detector  as  a  relay — the  power  used  in  making  sound 
in  the  telephone  coming  from  the  local  battery. 

Difficulties  surrounding  accurate  measurement  of  the  very  minute 
qu^tities  involved  make  the  above  statement  subject  to  modification. 
We  do  not  yet  know  exactly  how  a  detector  acta. 


166  MANUAL  OF.  RADIO   TELEGRAPHY  AND  TELEPHONY. 

RELAYS  OR  AMPLIPHONES. 

214.  The  amplifying  qualities  of  the  "  audion "  and  "  heterodyne " 
have  already  been  referred  to;  the  general  term  for  microphonic  and 
other  detectors  used  for  the  purpose  is  "  ampliphone/'  If  they  prove  to 
be  constant  and  reliable  they  will  be  supplied  for  general  use,  (a)  to  enable 
ordinary  messages  to  be  read  without  the  use  of  a  head  telephone,  (b)  as 
a  call,  (c)  to  increase  the  absolute  difference  between  signals  of  different 
strengths  thus  enabling  the  message  desired  to  be  read  through  inter- 
ference or  static,  (d)  to  step-up  signals  so  weak  that  they  could  not  other- 
wise be  read  and  thus  increase  the  range  of  communication,  (e)  as  a 
resonance  device  responding  within  limits  to  a  single  spark  frequency, 
thus  cutting  out  interference,  (f)  for  separating  signals  of  different 
wave  train  frequencies  or  different  wave  lengths  so  that  several  messages 
of  different  frequencies  can  be  received  at  the  same  time  on  the  same  aerial, 
(g)  to  automatically  record  incoming  signals. 

Coherer  detectors  change  their  resistance  sufficiently  to  work  a  relay 
which  actuates  a  call,  tapper  and  recording  apparatus.  Generally,  the 
induced  currents  rectified  by  crystal  and  valve  detectors  are  too  weak  to 
produce  visible  material  movement  unless  a  "  string "  galvanometer  is 
used  with  them.  The  same  is  true  of  the  direct  currents  produced  by  the 
momentary  depolarization  of  electrolytic  detectors. 

Rectified  currents  will  produce  sufficient  movement  of  the  diaphragm 
of  a  receiving  telephone  to  alter  its  pressure  on  a  microphonic  contact, 
this  alteration  being  enough  to  change  the  conductivity,  and  thus  increase 
or  decrease  the  current  in  a  circuit  containing  the  contact,  a  battery  and 
another  telephone.  This  change  in  current  moves  the  diaphragm  of  \he 
second  telephone  and  its  movements  can  either  be  read  directly  as  sound 
or  made  to  change  the  current  in  another  circuit  by  change  of  pressure 
on  another  microphonic  contact.  One  or  more  of  these  microphonic 
relays  produces  sufficient  action  in  a  loud  speaking  telephone  to  be  heard 
in  the  operating  room. 

When  used  as  a  resonance  relay,  the  relay  diaphragms  are  mounted 
so  as  to  have  a  pronounced  mechanical  period  of  vibration  and  act  as 
wave  filters  or  weeding  out  circuits,  responding  most  efficiently  only  to 
wave  trains  of  a  frequency  the  same  as  their  own.  The  sound  produced 
by  the  last  one  in  circuit  (the  loud  speaking  telephone)  may  be  intensified 
by  attaching  to  it  an  air  pipe  whose  note  is  the  same  as  that  of  the 
diaphragm  in  vibration.  The  microphonic  ampliphones,  just  described, 
have  not  proved  as  reliable  as  the  audion  ampliphone. 

RECORDING  APPARATUS. 

215.  Recording  apparatus  went  out  of  use  with  coherers.  It  is  possi- 
ble that  the  ampliphones  referred  to  in  the  preceding  article  will  again 
permit  the  use  of  both  recording  and  calling  apparatus.     Both  tend 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY.  167 

directly  to  economy  in  the  operation  of  wireless  stations,  by  reducing  the 
number  of  operators  to  a  minimum. 

It  has  already  been  found  possible  to  use  a  galvanometer  in  connection 
with  a  photographic  film  for  recording  transatlantic  messages. 

DIRECTION   FINDERS. 

216.  The  first  experimental  installations  of  direction  finders  have  been 
withdrawn,  it  not  being  found  practicable  to  operate  them.  The  principle 
on  which  they  operated  was  that  two  vertical  wires  parallel  to  the  plane  of 
movement  of  an  electric  wave,  if  half  a  wave  length  apart,  would  have 
electric  currents  of  opposite  phase  induced  in  them,  which  could  be  made 
to  double  the  receiving  effect  as  compared  with  a  single  wire,  while  if  at 
right  angles  to  the  plane  of  movement  of  the  wave,  the  induced  currents 
would  be  in  the  same  direction  and  could  be  made  to  neutralize  each 
other.  If  the  plane  of  this  direction  finder  pointed  towards  the  sending 
station,  the  strength  of  the  received  signals  would  be  a  maximum.  If  at 
right  angles  to  the  sending  station,  it  would  be  a  minimum. 

By  swinging  the  ship  in  azimuth,  the  compass  heading,  when  the 
strength  of  signal  was  a  maximum,  would  indicate  the  line  of  bearing  of 
the  sending  station.  The  practical  difficulty  in  the  way  of  operating  this 
system  to  the  best  advantage  is  the  very  short  waves  which  are  necessary 
on  account  of  the  comparatively  short  distances  that  can  be  obtained  be- 
tween wires  on  board  ship. 

Two  methods  of  determining  the  bearing  of  a  light-house  from  a  ship 
are  being  tried  out.  Both  depend  on  the  application  of  Marconi's  dis- 
covery (art.  188),  that  a  horizontal  aerial  sends  more  strongly  from  the 
direction  away  from  the  free  end  of  the  aerial,  and  receives  more  strongly 
from  the  direction  in  which  it  sends  best.  A  number  of  aerials  radiating 
from  the  sending  station  (light-house)  like  the  spokes  of  a  wheel,  are  in- 
stalled on  shore.  If  a  ship  sends,  the  spoke  on  which  her  signals  are  re- 
ceived the  strongest  is  the  one  having  the  same  bearing  from  the  light- 
house, as  the  light-house  has  from  the  ship.  If  the  light-house  sends,  it 
sends  on  each  aerial  in  succession,  on  a  time  schedule  known  to  all  ships. 
For  instance,  the  ship  knows  exactly  at  what  times  the  light-house  trans- 
mits from  the  aerial  bearing  north  from  the  light-house.  If  received 
signals  are  loudest  at  those  times,  the  light-house  bears  north  from  the 
ship. 

BELLINI-TOSI  WIRELESS  COMPASS. 

217.  Difference  in  the  planes  of  direction  of  two  similar  aerials 
makes  a  difference  in  the  strength  of  received  signals  whether  the 
distance  between  wires  is  half  a  wave  length  or  not.  And  this 
fact  is  utilized  in  the  Bellini-Tosi  apparatus  where  two  such  aerials  are 
installed  (see  fig.  63)  in  planes  at  right  angles  to  each  other  or  nearly  so. 
The  open  circuit  receiving  coils  are  mounted  so  that  they  make  the  same 


168 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


angle  with  each  other  as  their  aerials  and  their  angular  position  relative 
to  the  ship's  head  is  measured  and  shown.  The  closed  circuit  coil  can  be 
placed  in  the  plane  of  either  aerial  coil  or  in  any  intermediate  position. 
Its  plane,  relative  to  that  of  the  other  coils  when  the  strength  of  signals  is 
a  maximum,  is  approximately  that  of  the  passing  waves  and  is  indicated 
in  degrees  relative  to  the  ship's  head. 

PORTABLE  AND   AUXILIARY    SETS. 

For  the  requirements  of  auxiliary  sets  see  the  law  in  appendix  D. 
218.  Portable  sets,  as  their  name  indicates,  are  special  small  sets  which 
have  their  own  source  of  power,  such  as  a  foot  or  hand  operated  generator  or 


96.— N.  E 


Navy  Portable  Set. 


storage  battery,  and  when  used  on  shore  have  portable  masts  for  supporting 
the  aerial.  On  board  ship  this  single  wire  aerial  can  be  run  up  by  signal 
halliards,  and  if  insulated  wire  is  used  (since  portable  sets  work  usually 
at  low  voltages)  no  particular  care  need  be  taken  to  prevent  the  wire  from 
touching  the  mast,  deck  or  rigging. 

To  secure  good  results  with  portable  sets,  careful  tuning  is  required 
both  for  sending  and  receiving.  A  hot  wire  ammeter  and  wave  meter  are 
useful  adjuncts  of  portable  sets  as  well  as  of  those  of  larger  power. 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  169 

The  suit-case  type  illustrated  in  fig.  96  weighs  about  75  pounds  com- 
plete. It  has  a  motor  generator  for  ship  use,  which  lias  an  output  of  50 
watts  and  can  be  plugged  in  on  any  lighting  circuit.  Small  gasolene 
driven  generators  are  used  for  some  portable  shore  sets,  the  entire  send- 
ing and  receiving  apparatus  being  mounted  on  wheels.  The  power  or 
hand  operated  generator  set  of  the  suit-case  type  is  good  for  about  20 
miles.  A  complete  set  is  seen  with  condenser,  inductance,  and  key  in  the 
left  half;  motor  generator,  quenched  gap,  transformer,  and  receiving 
apparatus  in  the  right  half  of  the  case ;  with  the  plug  for  connecting  up 
with  the  lighting  or  power  circuit  at  the  upper  left-hand  corner. 

219.  To  illustrate  an  actual  wireless  telegraph  installation  the  station 
at  Sitka,  Alaska,  has  been  selected.  This  station  is  situated  on  Japonski 
Island  (see  frontispiece).  The  masts,  rigging  and  rigging  insulators, 
aerial  and  buildings  are  shown  in  fig.  97;  one  unit  of  the  generating 
sets  in  fig.  98;  the  receiving  apparatus  in  fig.  99.  These  figures  repay 
study  as  illustrating  a  neat  and  workmanlike  installation.  The  sending 
and  receiving  apparatus  is  after  the  designs  of  Professor  Pierce. 

Figs.  100  and  101  illustrate  actual  receiving  sets  of  other  types,  the 
elementary  diagrams  of  which  are  shown  in  figs.  83  and  86. 

The  construction  and  arrangement  of  both  sending  and  receiving 
apparatus  will  continue  to  vary,  but  a  careful  study  of  elementary  dia- 
grams (figs.  29  to  29e,  40  to  48  and  77  to  92)  in  connection  with  installa- 
tion diagrams  like  figs.  102,  103,  104,  105,  which  accompany  each  set  will 
enable  an  electrician  to  connect  up  and  operate  any  set  intelligently. 
There  are  too  many  types  of  apparatus  in  use  to  warrant  a  detailed 
description  or  illustration  of  each.  Such  description  and  instructions  are 
furnished  with  each  set.  This  manual  has  therefore  been  confined  to  the 
principles  common  to  practically  all  wireless  sets. 

AIRPLANE   RADIO    TRANSMITTER, 

The  first  airplane  set  used  in  the  navy  weighed  about  60  pounds  and  had 
a  sending  range  of  about  ten  miles.  The  set  was  tested  out  at  Annapolis, 
Md.,  in  1911.  A  counterpoise  antenna,  half  on  each  plane,  was  used  with 
this  transmitter.  The  power  was  supplied  from  the  propeller  shaft,  by  belt- 
ing to  the  radio  generator. 

In  1915  several  types  of  airplane  sets,  ranging  from  one-quarter  to 
one-half  K.  W.  were  tried  out  and  used  in  service.  The  apparatus  is 
mounted  on  the  fusilage  of  the  airplane,  in  front  of  the  observer,  in  order 
to  be  easily  operated.  A  small  generator,  propelled  by  a  wind-driven  fan, 
is  used  as  the  source  of  power.  A  counterpoise  antenna  is  used,  using  a 
trailing  wire.  The  weight  of  the  complete  set  is  approximately  100  pounds. 
Its  transmitting  range  is  roughly  75  miles. 


170 


MANUAL  OF   RADIO   TELEGRAPHY   AND  TELEPHONY. 


Fig.  97. 


MANUAL   OF   RADIO    TELEGRAPHY   AND   TELEPHONY.  171 


■          1 

Swif-    _ 

M                                      1     iJ        ■ 

1         ^^^ 

^B     l^f 

^ 

J                   r4=H  J 

TW\       ^H 

HpiP         fXn^ 

y7k:X\                                      1      Ulft' 

~T     \-V  ll               "^"^"J^ 

1      i^'iyW^               MyMj^ 

1  : 

■:. ^^minn 

M|tt| 

Fig.  97a. — Washington  Station. 


172  MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


173 


Fig.  97c. — Insulation  at  Base  of  One  Leg  of  Tower. 


174  MANUAL   OF   RADIO    TELEGRAPHY   AND   TELEPHONY. 


MANUAL  OF   RADIO   TELEGRAPHY  AND  TELEPHONY. 


175 


FiQ.  99. 


176  MANUAL    OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


Fig.  100. — ^Wireless  Telegraph  Receiver 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  177 

TO  AER/AL 


c-s^s^ vix£ 


^PARK  (SAP 


^^0^ 


AMMETER 


PRIMARY    REACTANCE 


KEyO={=&J- — 


TEZLEFUNKEN. 

Fig  102. 


5  ^         \XL ^ 


HOT  WIRE.  AMM- 


5HIP  MAINS 


CLOSED  CIRCUIT  OPEN   CIRCUIT 

INPUCTANCC.  INDUCTANCE 

FESSELNDEN 
FiQ.  103. 


12 


178 


MANUAL   OF   RADIO    TELEGRAPHY   AND   TELEPHONY. 


MANUAL  OF   RADIO   TELEGRAPHY  AND  TELEPHONY. 


179 


-*  ■* — I—*'  ♦■ 


Hi" 


iir 


Chapter  VIII. 

INSTALLATION,  ADJUSTMENTS  AND  MEASUREMENTS. 

INSTALLATION. 

220.  For  installation  ample  room  is  available  at  all  shore  stations. 

On  board  ship,  a  room  having  about  100  square  feet  of  floor  space, 
with  no  dimension  less  than  6  feet,  should  be  provided  for  the  installa- 
tion and  operation  of  a  wireless  telegraph  set.  The  operating  room 
should  be  well  ventilated  and  lighted,  as  nearly  sound-proof  as  practi- 
cable, and  free  from  vibration.  The  exact  location  of  the  room  is  not  of 
great  importance,  provided  a  good  lead  to  it  for  the  aerial  can  be  ob- 
tained.   The  farther  this  lead  is  from  large  conducting  bodies  the  better. 

The  room  should  have  a  well-insulated  entrance  for  the  aerial  and 
should  be  fitted  with  an  operating  table  about  2^  feet  wide,  not  less  than 
7  feet  long,  and  of  convenient  height  for  working  the  sending  key  while 
sitting  down. 

The  table  should  be  strongly  built  of  dry,  well-seasoned  wood. 

The  instruments  should  be  mounted  on  the  table  so  that  they  are  at 
safe  sparking  distance  from  each  other  and  from  any  part  of  the  oper- 
ating room. 

The  receiving  instruments  should  be  as  far  away  from  the  sending 
instruments  as  practicable.  The  induction  coil  or  transformer  may  be 
mounted  on  the  bulkhead  or  under  the  table.  In  any  case  it  should  be 
where  its  terminals  are  not  likely  to  be  touched  accidentally.  The  motor 
generator  is  preferably  installed  near  the  operating  room,  but  outside  of 
it.    It  may  be  installed  in  the  operating  room  or  in  the  dynamo  room. 

The  connections  between  all  parts  of  the  sending  and  receiving  instru- 
ments should  be  as  direct  as  possible,  and  in  the  case  of  sending  instru- 
ments they  should  be  of  large  surface  and  well  insulated  by  air  or 
other  nonconductors.  Sharp  turns  in  connecting  wires  should  be  avoided 
on  account  of  brush  discharges,  which  always  start  at  corners.  The  effect 
is  the  same  as  if  the  electricity  were  traveling  too  fast  to  turn  corners. 

The  necessity  for  bringing  a  number  of  leads  to  the  combination  switch 
for  sending  or  receiving  detracts  considerably  from  the  simplicity  of  the 
installation  and  to  a  slight  extent  from  the  efficiency  of  the  set  as  a  whole. 

High-potential  leads  should  be  kept  well  away  from  low-potential 
leads,  and  where  they  cross  it  should  be  nearly  at  right  angles. 


V  u 

Plate  1.— 600- Watt  Radio  Transmitter.    Front  View. 


PuiE  2.— 500-Watt  Radio  Transmitter.    Side  View. 


Plate  3.— 500-Watt  Radio  Transmitter.    Rear  View. 


Wiring  Diagram.  500-Walt  Transmitting  Set. 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


181 


The  ground  connections  should  be  electrically  good  and  of  large  area. 

The  receiver  (and  the  transmitter  when  practicable)  should  be  wired  up 
before  installation,  requiring  only  to  be  secured  in  place  and  attached  to 
aerial  and  ground. 

The  sending  appliances  should  be  so  arranged  that  the  leads  connecting 
the  condenser,  inductance,  and  spark  gap  of  the  transmitter  will  be  of 
minimum  length. 

At  shore  stations  means  should  be  provided  outside  the  operating  room 
for  disconnecting  the  aerial  from  the  operating  circuit  and  connecting  it 
direct  to  ground. 

On  board  ship  a  lightning  switch  should  be  installed  which  when  in 
use  will  safely  and  completely  disconnect  the  aerial  from  all  of  the  re- 
ceiver and  transmitter  circuits  and  connect  it  direct  to  ground. 

The  aerial  should  be  well  insulated  where  it  enters  the  operating  room 
and  where  it  passes  through  decks  or  bulkheads.  Porcelain  or  glass 
insulators  are  best  for  this  purpose. 

When  necessary  to  guy  the  aerial  at  any  point  an  insulator  should  be 
used  in  the  guy  line.  The  suspending  or  hoisting  halliards  of  the  aerial 
should  be  insulated.  Two  types  of  suitable  strain  insulators  for  this 
purpose  are  shown  m  figs.  106  and  107. 


FiQ.  106.— Aerial  Insulator— Buck  Link — Strain  10. 


Fig.  107.— Aerial  with  Locke  No.  105  Insulators. 


^«  "»^ 


rE  3.— 500-Watt  1 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


181 


The  ground  connections  should  be  electrically  good  and  of  large  area. 

The  receiver  (and  the  transmitter  when  practicable)  should  be  wired  up 
before  installation,  requiring  only  to  be  secured  in  place  and  attached  to 
aerial  and  ground. 

The  sending  appliances  should  be  so  arranged  that  the  leads  connecting 
the  condenser,  inductance,  and  spark  gap  of  the  transmitter  will  be  of 
minimum  length. 

At  shore  stations  means  should  be  provided  outside  the  operating  room 
for  disconnecting  the  aerial  from  the  operating  circuit  and  connecting  it 
direct  to  ground. 

On  board  ship  a  lightning  switch  should  be  installed  which  when  in 
use  will  safely  and  completely  disconnect  the  aerial  from  all  of  the  re- 
ceiver and  transmitter  circuits  and  connect  it  direct  to  ground. 

The  aerial  should  be  well  insulated  where  it  enters  the  operating  room 
and  where  it  passes  through  decks  or  bulkheads.  Porcelain  or  glass 
insulators  are  best  for  this  purpose. 

When  necessary  to  guy  the  aerial  at  any  point  an  insulator  should  be 
used  in  the  guy  line.  The  suspending  or  hoisting  halliards  of  the  aerial 
should  be  insulated.  Two  types  of  suitable  strain  insulators  for  thia 
purpose  are  shown  m  figs.  106  and  107. 


FiQ.  106.— Aerial  Insulator— Buck  Link— Strain  10. 


P^Q.  107. — Aerial  with  Locke  No.  105  Insulators. 


182 


MANUAL  OP   RADIO   TELEGRAPHY  AND  TELEPHONY. 


221.  The  large  momentary  currents  in  aerials  produce  large  inductive 
effects  in  conductors  near  and  parallel  to  them.  This  is  more  noticeably 
the  case  in  wire  stays  or  masts,  shrouds,  braces,  etc.  These  should  be 
grounded. 

It  should  also  be  noted  that  an  aerial  wire  parallel  and  near  to  a  long 
lighting  or  power  lead  may  induce  sufficiently  high  potentials  in  the  lead 
to  puncture  the  insulation  and  cause  sparking  between  it  and  other  con- 
ductors in  the  vicinity  of  combustible  material,  thereby  causing  fires. 
Or  it  may  puncture  the  insulation  and  cause  a  bum-out  of  an  armature, 
field,  or  transformer.  All  of  these  effects  have  been  experienced.  They 
are  especially  dangerous  to  the  wireless  sending  apparatus. 

PROTECTIVE   DEVICES. 

222.  Rigging  of  masts  at  shore  stations  is  divided  into  short  lengths  by 
strain  (usually  locust)  insulators.  Wire  braces  were  formerly  served  near 
the  middle  with  chokes  made  of  No.  26  B.  &  S.  soft  iron  wire  for  a  length 
of  about  10  feet,  the  object  being  to  ensure  that  no  conductor  of  approxi- 
mately the  same  natural  period  as  the  aerial  should  be  in  its  immediate 
viciniiy  (art.  195). 

Now  that  longer  wave  lengths  than  that  of  any  single  piece  of  ship's 
rigging  are  in  general  use,  it  has  been  found  beneficial  to  carefully  ground 
to  the  hull  all  metal  rigging,  a  slight  increase  in  the  effective  capacity  of 
the  aerial  resulting. 

Wire  leads  at  shore  stations  are  lead  covered  and  the  lead  grounded. 
Wires  in  conduit  on  board  ship  are  protected  by  the  conduit  being 
grounded. 

Wires  in  the  open  should  have  an  armored  cover  well  grounded. 

The  protective  devices  shown  in  fig.  108  are  installed  to  conduct  to 
ground  induced  high  potential  at 

(a)  Terminals  of  primary  of  transformers. 

(b)  Terminals  of  armature  of  alternator. 

(c)  Terminals  of  field  of  alternator. 

(d)  Terminals  of  shunt  field  of  motor. 

(e)  Terminals  of  armature  of  blower  motor. 


FUSE 


RESISTANCE 
VWNAA/\/WWW- 

I      25,000  OHMS 


Fig.  108. — Protective  Appliance. 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


183 


One  type  of  protective  device  consists  of  two  l-microfarad  condensers 
"  B  "  connected  in  series,  the  middle  connection  grounded  and  the  two 
outer  terminals  connected  by  strip  copper  leads  (as  short  as  possible)  to  the 
apparatus  to  be  protected.  In  parallel  with  each  condenser  is  a  per- 
manently set  spark  gap  "  C  "  between  .001  and  .003  inch  in  width.  Each 
leg  of  the  device  is  fused  with  a  3-ampere  cartridge  fuse  "  A."  A  resist- 
ance rod  "D"  (25,000  ohms),  with  its  middle  point  grounded,  is  also 
connected  across  the  line.    (See  figs.  108a  and  108c.) 

In  addition  to  the  above,  safety  spark  gaps  are  fitted  to  receiving  tele- 
phones.    Secondary  terminals  of  transformers  are  protected  by  chokes 


/7 


/7 


/9 


C/tOOA/O        ^T 


I 


Fig.  108a. 


made  from  the  leads,  and  by  safety  spark  gaps  permanently  set  at  the 
maximum  safe  sparking  distance.  Safety  spark  gaps  will  be  fitted  to  aerial 
insulators  at  stations  subject  to  lightning  strokes. 

The  usual  standard  protective  device  consists  of  two  0.05-microfarad 
mica  condensers  in  series,  connected  across  the  circuit  to  be  protected  with 
the  wire  joining  the  two  condensers  grounded.  No  fuse  or  protective  spark 
gap  is  used.  The  resistance  rod  is  also  no  longer  used,  on  account  of  the 
objection  to  grounding  the  direct  current  power  circuit  through  this  rod, 
thus  giving  a  "  ground  "  indication  on  the  ground  indicators  at  the  main 
switchboard.  Lugs  are  provided  on  bus  bars,  forming  part  of  the  pro- 
tective device,  the  lugs  on  one  end  being  marked  "  line  "  and  the  other 
end  "  apparatus."  Thus,  the  leads  to  the  apparatus  to  be  protected  pass 
through  the  protective  device;  hence,  if  the  protective  device  is  removed 
the  circuit  is  opened.    This  eliminates  the  possibility  of  disconnecting  the 


184  MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

device  and  leaving  the  apparatus  unprotected.  In  order  to  prevent  short 
circuits,  due  to  metal  being  placed  across  the  bus  bars,  the  entire  pro- 
tective device  is  covered  with  an  insulating  cover. 

A  photograph  of  this  type  of  protective  device  is  shown  in  fig.  108b. 

223.  All  wireless  telegraph  sets  are  fitted  with  a  multiple  switch  which 
in  the  sending  position  disconnects  the  receiving  circuits  from  the  aerial 
and  ground  and  breaks  detector  and  telephone  connections  as  may  be 
necessary  to  protect  them  from  induced  high  potentials. 

When  in  the  receiving  position  this  switch  opens  the  primary  or  sec- 
ondary circuit  of  the  transformer  and,  if  the  motor  generator  is  in  the 
operating  room,  operates  a  relay  for  opening  the  field  of  the  motor,  or  in 
some  cases  short  circuits  the  armature  to  bring  it  to  a  stop  quickly.  This 
switch  should  also  stop  the  blower  motor. 


Fig.  108b. 

The  necessity  for  the  above  detracts  considerably  from  the  simplicity 
of  an  installation. 

ADJUSTMENTS. 

224.  This  includes  calibration  and  tuning.  A  station  is  tuned  when 
both  sending  and  receiving  circuits  are  correctly  calibrated,  coupled  and 
adjusted  to  the  standard  damping  and  standard  wave  lengths.  Since  the 
periods  of  the  open  circuits  of  both  sending  and  receiving  sets  depend  on 
the  aerial  with  which  they  are  used  and  the  constants  of  the  latter  can  not 
usually  be  predetermined,  the  open  circuit  has  to  be  calibrated  after  the 
set  is  installed.  The  closed  circuit  of  receiving  sets  can  readily  be  cali- 
brated before  installation.  Also  the  closed  circuit  of  sending  sets,  if  wired 
up  before  installation. 

The  wave  length  of  a  circuit  made  up  of  a  calibrated  inductance  and 
a  calibrated  capacity  can  be  calculated  from  the  formula :  Wave  length  in 
meters  =  1884.9 5  VCL.  When  C  is  in  microfarads,  L  is  in  micro-henries, 
the  formula  being  derived  from  the  fundamental :    T  =  2TrVLC. 

For  calibrating  directly  in  wave  lengths  the  aerial  circuit  and  other 
circuits  not  already  calibrated,  wave  meters  are  supplied,  which  are  used 
as  receivers  to  calibrate  sending  circuits  and  as  senders  to  calibrate  receiv- 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY, 


185 


ing  circuits.  After  calibration  the  adjustment  of  these  circuits  to  the 
same  wave  length  and  to  the  desired  coupling  is  called  tuning. 

225.  To  be  completely  in  tune,  a  spark  sending  set  should  have  the  cir- 
cuit made  up  of  the  A.  C.  armature  winding,  primary  leads,  and  primary 
winding  of  transformer,  in  resonance  (tune)  with  that  formed  by  the 
sending  condenser  and  secondary  winding  of  the  transformer.  Both  cir- 
cuits should  be  in  resonance  with  the  alternator  frequency. 

The  closed  sending  circuit  should  be  in  resonance  with  the  open  cir- 
cuit and  the  coupling  and  decrement  of  the  open  circuit  such  as  to  afford 
the  necessary  selectivity  to  the  receiving  circuits  with  the  best  efficiency 
of  radiation. 


A 


rx 


L. 


I 


^ 


ilX 


Ofioi/^o      -"=" 


Fig.  108c. 


Receiving  circuits  to  receive  from  such  a  sender  should  be  in  resonance 
with  each  other  and  with  the  sending  circuits  and  should  have  the  same 
coupling  as  the  sending  circuits.  The  telephone  diaphragm  should  be 
in  resonance  with  the  wave  triain  (alternator)  frequency  and  with  the 
operator's  ear. 

As  was  previously  stated,  instead  of  designing  telephone  diaphragms 
for  resonance  with  alternators,  we  design  the  alternator  for  resonance 
with  the  telephone  diaphragm  or  with  the  human  ear. 

Resonance  is  thus  seen  to  be  a  vital  quality  in  wireless  telegraph  cir- 
cuits. (1)  Resonance  of  alternator  frequency  with  primary  sending 
circuit.  (2)  Resonance  of  primary  circuit  with  secondary  sending  cir- 
cuit. (3)  Resonance  of  closed  oscillating  circuit  with  open  radiating 
circuit.  (4)  Resonance  of  coupled  receiving  circuits  with  each  other  and 
with  coupled  sending  circuits.  (5)  Resonance  of  telephone  diaphragm 
with  primary  frequency.  (6)  Resonance  of  human  ear  with  telephone 
diaphragm. 

Of  these  (1),  (2)  and  (5)  are  elements  of  design  and  are  not  change- 
able at  the  will  of  the  operator,      (1)  and  (2)  can  be  varied  to  a  certain 


186  MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 

extent  by  reactance  regulators  which  in  some  sets  are  provided  for  both 
circuits;  but  it  is  preferable  to  cover  this  feature  in  the  original  design 
of  the  transformers.  (3)  and  (4)  are  entirely  under  the  operator's  con- 
trol and  on  them  the  efficiency  of  the  set  depends. 

MEASUREMENTS,  WAVE  METERS  AND  THEIR  USE. 

226.  Standard  calibrated  oscillating  circuits  called  wave  meters,  which 
are  adjustable  at  will  to  a  great  number  of  known  wave  lengths  are  used 
for  calibrating  and  tuning. 

When  adjusted  to  resonance  with  the  circuit  to  be  measured  the  fact 
is  indicated  according  to  the  type  of  wave  meter  by  a  maximum  of  sound 
in  a  telephone,  a  maximum  glow  in  a  vacuum  tube,  a  maximum  reading 
of  a  hot  wire  ammeter  or  the  brightness  of  a  glow  lamp. 

The  wave  meter  is  a  necessary  adjunct  to  every  radio  station.  It  is  a 
closed  oscillating  circuit  of  which  the  capacity  or  inductance,  or  both,  may 
be  varied.  It  is  very  carefully  calibrated  so  that  the  wave  length  corre- 
sponding to  any  capacity  and  inductance  used  may  be  read  directly  from  an 
attached  scale.  When  two  circuits  are  in  resonance  any  oscillations  set  up 
in  one  will  have  the  maximum  effect  in  the  other.  Thus,  by  placing  a  wave 
meter  near  any  oscillatory  circuit  and  varying  the  capacity  and  inductance 
of  wave  meter  and  thus  gradually  changing  the  period  of  the  wave-meter 
circuit,  the  current-indicating  device  will  give  its  maximum  indication 
when  the  two  circuits  are  in  resonance.  At  this  time  the  scale  of  wave 
meter  will  show  the  wave  length  of  the  resonant  circuits.  This  is  one  of  the 
principal  uses  of  the  wave  meter.  In  this  way  the  various  circuits  may  be 
calibrated  so  as  to  permit  the  use  of  any  wave  length  desired. 

The  wave  meter  may  be  used  as  a  receiver  when  any  form  of  detector  is 
included  in  its  circuit.  It  may  be  used  also  as  a  miniature  sending  set  with 
proper  means  of  exciting  it.  When  used  in  this  way,  it  may  set  up,  in  a 
nearby  oscillatory  circuit,  waves  of  any  desired  length  within  the  limits  of 
the  meter.  This  method  is  always  used  in  calibrating  the  receiving  circuit. 
The  Telefunken  wave  meter,  large  E.  G.  W.  type,  is  extensively  used  in  the 
naval  service. 

The  wave  meter  may  be  used  for  the  following  operations : 

1.  Tuning  and  measuring  wave  lengths  of  all  the  circuits  of  a  radio 
telegraphic  installation,  i.  e. : 

a.  The  closed  sending  circuit. 

b.  The  open  sending  circuit  (aerial). 

c.  The  closed  receiving  circuit. 

d.  The  open  receiving  circuit. 

2.  Testing  of  transmitter  tone. 


MANUAL   OF    RADIO   TELEGRAPHY   AND   TELEPHONY. 


187 


3,  Testing  of  detectors  for  sensitiveness. 

4.  Determination  of  capacity,  self-induction,  coupling  coefficients,  long- 
distance wave  lengths,  etc. 

The  Pierce  wave  meter  uses  a  telephone  exclusively.  It  is  suitable  for 
determining  resonance  only.  The  Donitz  meter  uses  a  hot  wire  ammeter 
or  air  thermometer,  whose  maximum  reading  indicates  resonance  and 
lower  readings  the  relative  amount  of  energy  received  when  the  wave 
length  of  the  wave  meter  is  varied.  These  readings  can  be  plotted  as  a 
curve.  Wave  meters  now  furnished  can  be  used  either  with  a  detector  and 
telephone  or  with  a  hot  wire  ammeter  or  galvanometer  for  determining 
resonance  and  making  other  measurements.  Wave  meters  are  also  fitted 
with  small  spark  gaps  and  spark  coils  so  that  they  can  be  used  as  senders 
for  calibrating  receiving  circuits.  Instructions  for  the  use  of  wave  meters 
are  supplied  with  the  instruments.     The  two  wave  meters  illustrated 


A  -  binOnc  posts. 
C  -  variablC  capocitt. 

D-  OrNiMOMLTCR. 

L-  INOUTANa. 

P  -  POINTER. 

T  -   SWITCH. 

L  -  LONG  WAVt  LENGTHS 

s  -  ShORT  WAVE  LENGTHS 


PiQ.  109. 


(figs.  109  and  110)  are  early  tj^es,  but  differ  only  in  details  from  those 
now  supplied. 


measur:ements  of  wave  lengths. 

227.  Fig.  109  shows  the  Pierce  wave  meter  referred  to  in  art.  226 
This  meter  is  used  for  calibrating  and  determination  of  resonance  by 
means  of  sound  only. 

Fig.  110  illustrates  the  original  Donitz  wave  meter  with  air  thermom- 
eter. A  hot  wire  ammeter  or  detector  and  galvanometer  are  now  used  with 
this  instrument. 

Instructions  for  the  use  of  the  Pierce  wave  meter,  which  follow,  are 
applicable  in  general  to  all  wave  meters. 


188 


MANUAL    OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


IIIHIIIIIIUIIIIIIH  ^  h 


FiQ.  110. — Slaby-Arco-Donitz-Wave  Meter. 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  189 

iNSTRDCTiaNS  FOR  USINQ  THE  PlERCE  WaVE  MeTER  OF  THE  MASSACHU- 
SETTS Wireless  Equipment  Co. 

A. — calibration  of  sending  station. 

1.  To  make  the  Instrument  ready  for  use. — Take  off  the  cover,  fold 
back  the  hinged  loop,  and  attach  the  leads  of  the  telephone  receiver 
(stowed  in  cover  of  box)  to  the  two  binding  posts  near  together  to  the 
left  of  the  metric  scale. 

2.  Placing  the  Instruments. — Place  the  instrument  near  the  circuit 
whose  wave  length  is  to  be  determined,  and  by  turning  the  loop  on  its  • 
projecting  horizontal  axis  bring  it  in  such  a  position  (parallel)  that  it 
will  be  linked  by  the  magnetic  lines  from  the  oscillating  circuit.  The 
proper  distance  from  the  loop  to  the  oscillating  circuit  depends  on  the 
intensity  of  the  oscillations.  When  the  observations  are  to  be  made 
directly  on  the  Leyden  jar  circuit  the  wave-meter  loop  may  be  one  or  two 
meters  from  the  discharge  circuit,  while  if  observations  are  to  be  made 
on  parts  of  the  circuit  in  which  the  currents  are  feebler,  this  distance  may 
be  reduced  to  a  few  centimeters. 

In  setting  up  a  station  the  wave  lengths  of  the  various  parts  of  the  cir- 
cuit may  be  determined  separately  in  the  usual  manner. 

When  the  station  is  already  set  up  ready  for  use,  the  wave  length  or 
the  two  wave  lengths  it  is  radiating  may  be  determined  by  placing  the 
wave  meter  near  the  wire  to  ground  or  the  wire  to  antenna  with  the  loop 
of  the  instrument  in  the  plane  of  the  wire. 

3.  Regulation  of  Spark. — Make  the  spark  of  the  station  short  and 
adjust  the  current  in  the  discharge  circuit  so  that  the  spark  is  clear  and 
sharp. 

4.  Taking  Observations. — Put  the  telephone  receiver  to  the  ear  and 
with  the  hand  holding  the  receiver,  touch  one  of  the  metallic  tips  of  the 
lead  where  it  enters  the  receiver.  This  will  shut  out  the  general  hum  due 
to  the  alternating  current  in  the  transformer.  If  no  such  hum  is  present 
it  is  not  necessary  to  touch  the  terminal  in  this  manner. 

Now  with  the  free  hand  turn  the  handle  in  the  center  of  the  instru- 
ment and  set  for  a  maximum  in  the  telephone. 

In  making  these  observations  the  switch  to  the  right  must  be  either 
on  "  L  "  or  "  S."  This  switch  should  be  on  "  L  "  for  long  waves  and  on 
"  S  "  for  short  waves.  With  the  switch  on  "  S  "  read  the  position  of  the 
pointer  or  red  scale.  The  position  of  the  pointer  for  a  maximum  sound 
in  the  telephone  is  the  wave  length  in  meters.  If  the  switch  is  on  "  L'* 
the  black  scale  should  be  read  and  gives  the  wave  length  in  meters. 

In  case  the  sounds  in  the  telephonic  receiver  are  too  loud  for  accurate 
settings,  their  intensity  may  be  reduced  either  by  moving  the  instrument 
farther  away,  or  more  conveniently,  by  turning  the  receptor  loop  so  that 


190  MANUAL   OF    RADIO   TELEGRAPHY   AND   TELEPHONY. 

the  inductive  action  is  diminished.    In  the  final  setting  it  is  desirable  to 
have  the  sound  in  the  telephone  just  audible  at  resonance. 

5.  Use  of  Geissler  Tube  for  Demonstrations. — If  it  is  desired  to  use  a 
Geissler  tube  with  the  instrument,  leave  the  telephone  connected  in,  con- 
nect one  terminal  of  the  tube  to  the  nearer  left-hand  post  along  with  the 
telephone  lead  and  the  other  terminal  of  the  tube  to  the  idle  binding 
post  at  the  back  of  the  instrument.  The  tube  is  then  in  parallel  with 
the  condenser  of  the  wave  meter  and  should  glow  at  the  proper  setting. 

B. — CALIBRATION    OF   RECEIVING    STATION. 

6.  Use  of  Wave  Meter  as  Sending  Station. — Take  off  the  telephonic 
receiver  of  the  wave  meter  and  put  in  its  place  the  spark-gap  supplied  with 
the  apparatus.  This  attachment  has  a  coil  in  its  base  of  approximately 
the  proper  inductance  to  replace  the  telephone.  Use  the  wave  meter  as  a 
sending  station  and  for  any  given  wave  length  of  the  wave  meter  set  the 
receiving  station  to  resonance  as  in  receiving  messages  from  a  distant 
source. 

7.  SparJc-Coil. — In  using  the  wave  meter  as  a  sending  station  it  should 
be  actuated  by  a  small  spark-coil.  Attach  the  leads  from  the  secondary 
of  the  spark-coil  to  the  two  sides  of  the  wave  meter  spark-gap.  This  gap 
should  be  opened  not  more  than  a  few  hundredths  of  an  inch  (.1  or  .2 
millimeters).  When  the  gap  is  too  wide,  sparks  occur  inside  the  wave 
meter  between  the  plates  of  the  condenser. 

8.  Position. — The  wave  meter  when  used  as  a  sending  station  should 
be  placed  about  three  meters  from  the  receiving  antenna,  and  should  not 
be  approached  too  closely  by  the  observer  who  is  listening  at  the  telephone 
of  the  receiving  station,  since  conduction  or  induction  through  the  body 
of  the  observer  and  along  his  telephone  leads  will  result  in  a  general  hum 
that  can  not  be  tuned  out. 

C. — PRECAUTION  AND  CARE  OF  THE  INSTRUMENT. 

9.  Do  not  attempt  to  open  the  telephone  receiver,  and  do  not  change  or 
break  the  leads  of  the  telephone  as  injury  to  the  telephone  will  disturb  the 
calibration.  Due  to  climatic  conditions  and  other  causes  all  wave  meters 
are  subject  to  changes  of  characters.  They  should  be  frequently  checked 
with  a  standard  meter  and  errors  noted. 

10.  In  stowing  away  the  apparatus  be  careful  to  leave  the  pointer  free 
from  obstructions.  To  this  end,  whenever  the  instrument  is  to  be  trans- 
ported it  is  advisable  to  disconnect  the  telephone  and  place  it  in  the  clamp 
in  the  cover  of  the  box  with  the  leads  secured  under  the  wooden  buttons. 

11.  The  receptor  loop  should  be  folded  in  with  hnob  upma/rd  so  thai 
pointer  can  he  rotated  under  the  loop  without  interference. 


MANUAL   OF   RADIO   TELEGRAPHY   AND   TELEPHONY.  191 

228.  In  determining  wave  lengths,  three  methods  for  fixing  the  con- 
denser reading  for  maximum  current  may  be  used.  1.  For  a  rough 
determination  the  apparent  position  of  maximum  reading  may  be  fixed 
by  a  single  observation.  2.  For  a  more  accurate  determination  the  maxi- 
mum reading  of  the  hot-wire  ammeter  or  galvanometer  may  be  noted, 
and  the  condenser  pointer  be  moved  first  to  the  right  until  the  current 
reading  falls  by  a  certain  amount,  and  then  to  the  left  of  the  maximum 
position  until  it  falls  to  an  equal  amount.  The  position  half  way  be- 
tween these  two  condenser  readings  may  be  taken  as  the  true  maximum. 
3.  The  values  of  the  current  reading  corresponding  to  a  large  number  of 
condenser  readings  on  each  side  of  the  maximum  may  be  taken,  and  a 
curve  plotted  having  condenser  readings  as  abscissas  and  current  readings 
as  ordinates.  From  this  curve  the  most  accurate  possible  position  of  the 
maximum  can  be  obtained. 

For  measuring  the  wave  length  of  any  sending  set  as  it  is  being  used 
it  is  only  necessary  to  bring  the  wave  meter  into  position  near  a  single 
loop  in  either  the  antenna  or  ground  connection,  taking  care  that  there 
is  no  direct  induction  from  the  helix  into  the  wave  meter  coil,  close  the 
key  for  a  long  dash  and  ascertain,  by  moving  the  pointer  over  the  grad- 
uated scale,  the  position  of  resonance  as  indicated  above,  i.  e.,  by  tele- 
phone H.  W.  A.  (hot-wire  ammeter)  or  galvanometer.  This  will  gen- 
erally be  on  the  longer  wave  or  "  upper  hump  "  since  in  stations  sending 
out  two  waves  the  longer  wave  contains  the  most  energy  and  is  the  most 
easily  read.*  To  locate  the  short  wave  ("  lower  hump  ")  it  may  be  neces- 
sary to  couple  the  wave  meter  helix  quite  closely  with  the  loop.  In  seta 
having  loose  coupling  and  those  supplied  with  quenched  spark  gaps,  hut 
one  position  of  resonance  should  he  found. 

To  ascertain  the  wave  length  of  the  closed  circuit,  disconnect  the  aerial, 
couple  the  wave  meter  with  the  helix  and  proceed  as  before.  But  one 
wave  length  vdll  be  found.  This,  if  the  same  as  the  first  one  measured, 
will  show  that  there  is  but  one  length  of  wave  being  generated  and 
radiated.  The  two  operations  above  described  can  be  performed  in  less 
than  five  minutes.  To  ascertain  the  wave  length  of  the  aerial  is  not  so 
easy.  To  do  so,  disconnect  the  closed  circuit,  place  a  temporary  spark 
gap  in  the  ground  lead  of  the  aerial,  connect  leads  from  the  transformer 
to  each  side  of  the  gap  and,  in  ordinary  ship  sets  where  the  capacity  of 
the  aerial  is  small,  also  put  a  Leyden  jar  across  the  gap.  Place  the  wave 
meter  near  the  aerial  inductance  and  adjust  to  resonance.  This  reading 
should  be  the  same  as  that  found  for  the  closed  circuit.  The  above  meas- 
urements will  show  whether  the  open  and  closed  circuits  are  in  resonance 
and  what  wave  length  or  lengths  are  being  sent  out. 

*  See  law  relating  to  use  of  "  pure  wave,"  p.  248. 


192  MANUAL    OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 

A  rapid  way  to  adjust  a  transmitter  is  to  tune  the  closed  circuit  to  the 
desired  wave  length  with  a  wave  meter  and  then  tune  the  open  circuit  to 
resonance  with  the  hot  wire  ammeter,  but  this  has  its  limitations  (see  arts. 
230  and  340). 

229.  If  both  open  and  closed  circuits  read  425  meters  and  the  upper 
hump  is  found  to  be  450  and  lower  hump  390,  the  percentage  of  coup- 
ling *  is 

450-390 

425  ^*"^- 

If  but  one  hump  is  found  and  that  at  425,  with  an  ordinary  spark  gap, 
the  circuits  are  very  loosely  coupled.  This  fact  can  also  be  determined 
approximately  by  an  inspection  of  the  sending  helix.  If  direct  con- 
nected and  but  one  wave  length  is  found,  it  will  also  be  found  that  the 
number  of  turns  common  to  the  two  circuits  is  very  small  or  less  than 
one  turn.  If  inductively  connected,  that  the  active  parts  of  the  two 
helices  are  not  close  together,  in  other  words,  the  mutual  induction  is 
very  small.  The  single  wave  found  on  loose  coupled  sets  using  an  ordi- 
nary gap  is  not  as  sharp  as  that  found  on  the  closed  circuit  read 
separately.  Some  mutual  induction  is  necessary  to  transfer  energy  so 
thai  the  two  waves  can  not  quite  merge  into  one. 

TUNING  CURVES. 

230.  Tuning  curves  showing  the  wave  length  for  any  adjustment  of 
each  circuit  should  be  made,  plotting  the  wave  meter  readings  as  wave 
lengths  (horizontally)  on  the  bottom  of  a  sheet  of  cross  section  paper 
(standard  A  sheet)  and  the  number  of  turns  of  the  helix  for  each  read- 
ing on  the  side  (vertically). 

Draw  smooth  curves  (fig.  Ill,  curves  (1)  and  (2)  and  fig.  115,  curves 
marked  "aerial"  and  "exciting")  through  the  points  thus  found  for 
both  the  open  and  closed  circuits.  An  inspection  of  these  curves  will 
show  how  many  turns  of  the  helix  must  be  included  in  each  circuit  for 
any  given  wave  length.  When  set  by  these  tuning  curves  to  the  same 
wave  length  the  accuracy  of  the  curves  can  be  checked  by  the  reading  of 
the  H.  W.  A.  If  the  setting  is  correct,  any  change  of  inductance  or 
capacity  in  either  circuit  will  decrease  the  reading  of  the  H.  W.  A.  It 
must  be  remembered  as  stated  elsewhere  that  it  generally  takes  a  change 
of  several  turns  of  inductance  to  change  the  wave  length  of  the  open 
circuit  appreciably,  while  a  change  of  less  than  one  turn  will  change  the 

*  Percentage  of  coupling,  as  defined  above,  differs  from  coeflBcient  of  coup- 
ling, which  is  defined  as  the  ratio  of  the  mutual  induction  of  two  circuits 
to  the  square  root  of  the  product  of  their  respective  self  inductions  or 

M 

— 7=  —  coeflBcient  of  coupling. 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONT. 


193 


»v<» 

f«     /< 

tngfh 

.  Mmtors. 

Oi 

^. 

r- 

1 

1 

i 

1 

1 

1 

I 

/ 

I-" 

§ 

s 

o 

s 

^ 

5 

V 

V 

< 

>>- 

\ 

\ 

/ 
/ 
/ 

• 

— 1 

\ 

'5 

\-*---5 

1 
1 
I 

; 

^ 

1=^ 

\" 

\ 

V 
\ 

\ 
-5^ 

1 

'•'C-> 

?*'> 

1 

'^^ 

\ 

\ 

/-• 

=o^^ 

'1   - 

""■~-  .. 

■ 

5: 

P— 

Ce^/>/. 

•fl-     vf^. 

fam 

''-. 

'"-*. 

<■ 

;^ 

—  ^ 

1 

,^ 

■»\- 

(f 

<• 

'«• 

31 

\7 

I 
r 

« 

1 

f 

1 

1 

^ 

\ 

O 

c 

S 

/ 

N 

^\- 

V 

f . 

\ 

5 

< 

• 

z 
> 

5 

1 
1 

1 

\ 

Vi 

\ 

r 

0 

3 

oa 

z 

> 

o 

A 

1 
1 

1 

\ 

\ 
\ 

1 

3- 

$ 

"i 

1 
/ 

i 

M 

\ 

\^ 

\ 
\ 
\ 

I 

> 
7 

0 

n 

r 

( 

/ 
/ 

\ 

■v 

,/ 

0     n 

• 

3 

Q. 

01 

e 

1 

1 

1 

>* 

\ 

\ 
\ 
\ 

/ 

^    3 

O 
0 

c 

■0 

r 
m 

Cb 

f 

1 
1 
1 

r 

X 

§4 

9X 

3 

oa 
o 

> 

Is 

1 
1 

>* 

V 

/ 

/   ^ 

\ 

v^ 

a 
• 

c 

< 

n 

\ 

1 

% 

/ 

/ 

\ 

s.  '^ 

\ 

o 
z     -^ 

/ 

/ 

\ 

\^ 

s 

/ 

( 

1 

i  1 

K 

?     / 

/ 

\ 

s 

s 

t-1 

/^o^  AK/z-e    Ammefar      Sca/c  Oer/. ....  •#  Oct/ a.  •  /  /4/»jo 


13 


194  MANUAL    OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 

wave  length  of  the  closed  circuit  considerably,  so  that  it  is  much  easier  to 
throw  the  two  circuits  out  of  resonance  by  changing  the  closed  circuit 
turns  than  by  changing  the  open  circuit  turns. 

It  must  also  be  remembered  that  the  tuning  curve  for  a  closed  circuit 
is  only  correct  for  the  capacity  in  the  circuit  at  the  time  the  measure- 
ments were  made.  ^ 

The  removal  of  a  jar  from  the  condenser;  change  of  shape  or  length 
of  leads  to  helix;  bad  connections  to  jars — each  and  all  change  the  wave 
length  of  the  closed  circuit  and  throw  it  out  of  resonance  with  the  open 
circuit  with  marked  decrease  in  radiation. 

The  H.  W.  A.  can  be  used  to  adjust  two  circuits  to  the  same  wave 
length  but  it  gives  no  indication  of  what  that  wave  length  'is. 

When  a  wave  meter  is  available,  it  is  shown  above,  that  to  take  a  reading 
of  the  closed  circuit  wave  length  requires  but  a  minute's  work. 

The  wave  length  of  the  open  circuit  with  the  same  number  of  turns 
included  varies  little  from  any  cause,  and  if  the  insulation  and  ground 
are  good  the  causes  of  decreased  radiation  should  be  looked  for  in  the 
spark  gap  or  in  bad  connections,  broken  jars,  etc.,  in  other  parts  of  the 
closed  circuit. 

It  has  been  proposed,  where  the  coupling  is  such  that  two  wave  lengths 
are  radiated,  to  throw  the  two  circuits  slightly  out  of  resonance  in  order  to 
increase  the  proportion  of  the  total  energy  in  the  long  wave ;  but  no  dis- 
tinct gain  in  efficiency  has  been  noted. 

It  is  better  to  loosen  the  coupling  to  the  point  where  but  one  wave  can 
be  found,  even  if  this  is  beyond,  as  it  usually  will  be,  the  point  where 
the  highest  hot  wire  ammeter  reading  is  obtained. 

It  must  be  remembered,  however,  that  efficiency  varies  directly  as  the 
H.  W.  A.  reading  and  the  latter  must  be  maintained  as  high  as  possible 
consistent  with  sending  out  waves  of  but  one  length. 

231.  In  calibrating  closed  sending  circuits,  the  shape,  as  well  as  the 
length  of  the  leads,  must  be  taken  into  consideration.  This  shape  must  be 
the  permanent  one.  In  sets  now  being  supplied  connections  with  the  helix 
or  spiral  are  made  so  as  to  avoid  any  change  of  shape  with  change  of  wave 
length. 

In  calibrating  the  open  circuit  of  receiving  sets  the  same  difficulty  will 
be  found  in  obtaining  sharp  resonance  as  when  calibrating  open  sending 
circuits. 

Calibrating  sending  and  receiving  circuits  enables  us  to  select  and  send 
and  set  our  instruments  to  receive  definite  known  wave  lengths  and  is  the 
first  requisite  of  tuning.  In  order  that  our  receiving  circuits  may  be 
selective,  i.  e.,  respond  only  to  the  wave  lengths  for  which  they  are 
adjusted  they  must  have  comparatively  large  self-induction.  In  other 
words,  they  must  be  what  are  known  as  stiff  or  rigid  circuits.    In  order 


MANUAL   OF    RADIO    TKLEGRAPIIY    AND    TELEPHONY. 


195 


aeo     2.60 


Z70        2B0      2.30       300        3IO         320       330       ^M-O      350      360       37o     3BO      3&0 

WAVE   LENGTHS  IN  METERS 

Fio.  112. 


196  MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 

that  a  wave  train  may  be  long  enough  to  build  up  current  in  a  rigid  re- 
ceiving circuit  the  sending  circuit  must  be  a  persistent  oscillator,  i.  e.,  it 
must  be  slowly  damped.    (Fig.  18h.) 

It  must  not  be  forgotten  that  the  currents  in  a  very  persistent  oscilla- 
tor like  a  closed  sending  circuit  are  mostly  dissipated  in  heat,  while  we 
wish  to  have  their  energy  radiated  in  electric  waves. 

We  must  therefore  strike  a  mean  between  the  efficient  very  highly 
damped  sending  circuit  which  radiates  nearly  all  the  energy  it  receives 
in  one  or  two  waves,  but  which  affects  all  receiving  circuits  alike  and  the 
inefficient  persistently  oscillating  sending  circuit  which  dissipates  most 
of  its  energy  in  heat  but  which  is  favorable  for  selective  receiving. 

Sharp  tuning  or  selectivity  depends,  therefore,  on  self-induction  in  the 
radiating  circuit  as  well  as  in  the  receiving  circuits. 

232.  The  air  thermometer  readings  in  the  wave  meter  measure  the 
received  current  in  the  same  way  that  a  hot  wire  ammeter  in  the  aerial 
measures  the  sending  current.  The  readings  of  both  meters  vary  accord- 
ing to  the  heat  generated  by  the  currents  and  this  heat  varies  as  the  square 
of  the  current. 

Dr.  Austin  finds  that  the  loudness  of  signal  in  a  receiving  telephone  is 
proportional  to  the  square  of  the  current  and  that,  if  a  rectifying  detector 
and  galvanometer  are  used  for  measuring  the  received  currents,  the  galva- 
nometer deflections  are  also  proportional  to  the  square  of  the  oscillating 
currents ;  so  all  these  ways  of  measuring  are  directly  comparable. 

RESONANCE  AND  AUDIBILITY  CURVES. 

233.  Eeferring  to  the  first  paragraph  of  art.  228,  the  third  method  given 
for  determining  the  position  of  maximum  current  in  the  receiving  circuit 
(wave  meter),  and,  therefore,  the  position  of  resonance  between  the  wave 
meter  circuit  and  the  transmitting  circuit  results  in  a  curve  which  may  be 
called  a  resonance  curve. 

Eesonance  curves  are  illustrated  in  figs.  Ill  to  116  and  particularly  in 
Figs.  113  and  114. 

In  fig.  113  the  wave  meter  condenser  readings  are  laid  off  horizontally 
to  scale  (these  are  the  abscissas  of  points  in  the  curve).  The  correspond- 
ing hot  wire  ammeter  or  galvanometer  readings  are  laid  off  vertically 
(these  are  the  ordinates  of  points  in  the  curve) .  Instead  of  the  condenser 
readings,  we  might  use  directly  the  wave  lengths  which  they  represent,  and 
instead  of  the  galvanometer  readings,  we  might  use  multiples  of  the  least 
current,  which  would  make  a  signal  readable,  or,  rather,  multiples  of  the 
least  received  power  (see  table  8,  appendix  A),  which  would  make  a  signal 
readable. 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


197 


Power  and  audibility  are  proportional  to  the  galvanometer  readings,  so 
that  the  shape  of  the  curve  would  not  be  changed  and  it  might  be  called 
an  audibility  curve  as  well  as  a  resonance  curve. 

234.  Audibility  curves  can  ])e  plotted  with  any  calibrated  receiving  set 
as  well  as  with  a  wave  meter.    The  wave  length  at  the  lower  or  upper 


A  =  750  M. 


Sl  +  6  =  0  038. 


bU 

r 

r— 1 

r\ 

/ 

50 

/ 

] 

/ 

40 

/ 

/ 

/ 

'^f 

30 

\ 

20 

\ 

\ 

]| 

y 

\j 

10 

\ 

\ 

/ 

\ 

/ 

/ 

\ 

/ 

/ 

V 

/ 

^8 

4 

9 

5 

0 

5 

I 

5 

a 

CONDENSER  SETTING  IN    DEGREES. 

FiQ.  113. — Resonance  Curve  Taken  with  Wave  Meter. 

limit  of  audibility,  divided  by  the  resonant  wave  length,  might,  when 
receiving  from  a  standard  transmitter  at  a  standard  distance,  be  called 
the  figure  of  merit  of  a  receiving  set,  an  indication  of  its  selectivity. 

Or  if  the  same  receiving  set  is  used,  the  audibility  or  resonance  curves 
of  different  transmitters  are  a  means  of  comparing  their  dampings  and 
their  suitability  for  selective  receiving  might  be  said  to  give  the  figure  of 


198  MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 

merit  of  the  transmitters.  For  instance,  in  curve  7,  fig.  Ill,  and  curve  III, 
fig.  112,  let  the  portion  above  the  heavy  line  X  Y  represent  the  range  of 
audibility  at  any  distance,  say  100  miles  from  the  transmitter. 

In  curve  7  a  change  of  150  meters  on  either  side  of  the  position  of  maxi- 
mum loudness  (resonance)  would  be  required  to  render  signals  inaudible, 
while  from  the  transmitter  of  curve  III  a  change  of  only  12  meters  either 
way  from  the  position  of  resonance  would  cut  out  signals. 

Since  the  same  or  similar  wave  meters  were  used  in  plotting  these  curves, 
we  conclude  that  the  difference  in  their  shape  is  due  to  differences  in  the 
transmitters,  and  that  the  transmitter  of  fig.  112  is  a  more  persistent 
oscillator  than  that  at  Guantanamo  (fig.  Ill) . 

The  maxima  of  these  curves  have  no  direct  relation  to  each  other,  since 
they  are  produced  by  different  amounts  of  radiated  energy  and  different 
relative  positions  of  the  wave  meter  and  transmitting  circuits. 

It  is  their  shapes  alone  which  are  the  subject  of  comparison  and 
discussion. 

The  shape  of  each  curve  will  remam  the  same,  whatever  the  position  of 
the  receiving  circuit. 

In  neither  of  the  curves  under  discussion  would  the  lower  hump  audibly 
affect  the  receiving  apparatus. 

235.  Where  audibility  changes  rapidly  with  small  change  of  wave 
length,  the  circuits  are  said  to  be  sharply  tuned. 

It  will  be  noted  from  the  resonance  curve  of  the  aerial  (fig.  112)  that 
sharp  tuning  with  it  alone  is  not  possible,  but  that  when  coupled  with  the 
persistently  oscillating  closed  circuit,  the  transmitter  as  a  whole  gives 
fairly  sharp  resonance.  There  is  no  more  possibility  of  an  escape  from  a 
whip-crack  transmitter  than  from  static. 

It  is  found  that  the  shape  of  resonance  curves  depends  on  the  damping 
of  the  receiver  as  well  as  that  of  the  transmitter,  and  that  sharp  curves, 
like  those  in  figs.  113  to  116,  cannot  be  obtained  without  a  stiff  receiving 
circuit  loosely  coupled  (par.  239). 

236.  The  resonance  curves  of  figs.  Ill,  112, 115  and  116  are  from  direct 
connected  transmitters. 

The  transmitter  of  fig.  115  was  so  loosely  coupled  as  to  give  but  one 
hump  in  the  curve. 

The  transmitter  of  fig.  116  has  a  quenched  gap.  The  lower  hump 
(curve  II),  shown  at  about  860  meters,  and  the  flat  part  of  the  curve,  at 
1075  meters,  may  indicate  the  energy  radiated  while  building  up  (fig.lSh) 
before  the  transfer  of  energy  to  the  open  circuit  is  complete.  The  percen- 
tage of  coupling  indicated  by  these  two  humps  is  22  per  cent,  but  by  far 
the  largest  part  of  the  energy  is  radiated  at  the  natural  period  of  975 
meters.     (The  two  curves  in  this  figure  have  a  different  scale  of  ordinates, 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


199 


CURVE!  1_  wave:    L-CMCSTH         DAtS/1P'|M<3 

I  SF'ARK  3S10  .021 

2  AEC  2   COIL-S  SS20     DIRCCT  .OlS 


1 

1 . 

2 

"• 

J35.4-** 

1 

'      1 

/y 

v_ 

V 

cucve.  -I 
cuizvEi  -  a 


5A- 
129 


S6 

131 


S8 

133 


e,o 

62 

135 

137 

'10.  114. 

66 


68 
14-3 


200  MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

60  that  their  coincidence  is  only  apparent.  The  maximum  readings  are 
in  reality  smaller  for  the  open  than  for  the  closed  circuit.) 

237.  The  resonance  curves  in  fig.  114  are  (curve  1)  from  a  feebly 
damped,  inductively  coupled  transmitter,  with  a  synchronous  spark  gap, 
and  (curve  2)  from  an  undamped  arc  transmitter,  with  the  arc  directly 
in  the  open  circuit. 

Theoretically,  all  the  damping  of  curve  2  should  be  due  to  the  receiver, 
but  slight  inequalities  in  wave  lengths  emitted  by  the  arc  can  be  found, 
which  have  the  effect  of  an  apparent  damping;  it  tends  to  broaden  the 
resonance  curve. 

As  has  already  been  stated,  on  account  of  the  time  required  to  properly 
adjust  the  arc,  arc  sending  sets  are  in  operation  all  the  time,  sending  con- 
sisting only  of  change  of  wave  length,  so  that  they  can  be  tuned  in  on  the 
wave  length  of  the  intervals  instead  of  the  dashes  and  dots. 

On  account  of  the  very  steep  resonance  curves  of  such  transmitters,  when 
the  range  of  audibility  is  near  the  upper  part  of  the  curve,  it  is  very  easy 
to  miss  when  tuning,  i.  e.,  a  sharply  tuned  transmitter  is  more  difficult  to 
find  than  a  broadly  tuned  one,  unless  its  wave  length  is  known  exactly. 

MEASUREMENT  OF  DAMPING. 

238.  In  addition  to  being  able  to  estimate  damping  from  tuning  or 

resonance  curves  we  can  measure  it  directly  as  follows ; 

72 
It  was  stated  that  the  damping  of  any  circuit  8=  ^-y  ,  where  R  is  the 

resistance,  n  the  frequency  and  L  the  self-induction  of  the  circuit.  The 
theory  of  coupled  circuits  shows  that  the  sum  of  the  damping  of  the 

C   —C      I       P 
two  circuits  8i  +  82  =  7r    — 7^ iJ  -^2   _n     »  where  Cm  represents  the 

position  of  the  condenser  in  degrees  for  most  perfect  resonance,  and 
Im  the  maximum  current  in  the  second  circuit  corresponding  to  the 
position  of  the  condenser  Cm,  and  where  I  represents  the  current  in 
the  circuit  corresponding  to  any  other  position  C  of  the  variable  con- 
denser. This  formula  becomes  much  simplified  for  practical  purposes, 
and  gives  in  general  accurate  enough  results,  if,  instead  of  plotting 
a  complete  curve,  we  change  the  variable  condenser  so  that  for  the 
reading  C,  I*=i  Pm-     The  quantity  under  the  radical  then  becomes 

C   —G 
unity,  and  8i-f-82  =  7r  ^^^ .     Two    values  of  C  should  be  observed, 

one  on  each  side  of  Cm,  and  the  mean  of  the  two  values  of  the  damping 
taken.  If  the  current  is  measured  by  means  of  a  thermo-element  or  a 
perikon  detector  in  connection  with  a  galvanometer,  the  readings  of  the 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


201 


""■ 

■~~ 

""" 

1 

—~ 

—"" 

— 

1 

— 

— 

"^ 

T 

i 

1 

i 

• 

s 

u 

n 

! 

<5 

V 

z 

S 

_i 

S) 

J 

rt 

I 

»!** 

5 

$ 

(0 

sc 

5 

3 

J^ 

IS 

c/i 

-1 

? 

vi 

1 

? 

oc 

(0 

J 

f 

$ 

1 

' 

5 

S 

i 

1 

\ 

«c 

s 

>• 

\ 

< 

1 

' 

^ 

1 

\ 

i 

z 

hi 

> 

s. 

( 

s 

J 

1 

\ 

\, 

I 

M 

u 

\ 

1 

1 

\ 

1 

5 

s 

^ 

If 

s 

if 

'    1 

" 

'V^ 

/^ 

1 

1 

^ 

i 

» 

1 

If 

u 

N 

s 

i 

z 

\ 

>    1 

* 

(3 

> 

V 

S 

1 

\ 

1 

■ 

> 

> 

N 

s. 

2 

t 

\ 

X- 

5= 

> 

5 

\ 

V 

U 

-<- 

\ 

3 

1' 

ridi 

^1 

i 

S 

< 

V 

I 

4 

g 

\ 

V 

1 

< 

•« 

> 

itua. 

V 

^ 

___ 

_ 

-^ 

s. 

■n 

— 

3» 

It 

» 

^ 

^ 

N 

s. 

V 

« 

k 

V 

z 

(A 

g 

^ 

> 

s 

\ 

« 

i^ 

f— 

*i  tt\ 

1 

^ 

n 

i 

^ 

ft-^ 

\ 

il 

V 

Ot'M 

i^if^ 

t 

$ 

^ 

'^ 

s. 

i^\ 

y/  1 

tf 

1 

s 

s 

(t 

s 

^s 

*** 

"- 

? 

uni 

^  >- 

rib 

i 

1 

9 

? 

< 
h 

"^ 

•«« 

- 

i  - 

^ 

2 

«/i 

i 

3 

i 

\ 

- 

w 

a 

k 

•> 

K 

«> 

•■ 

• 

ii 

♦ 

h 

•< 

202  MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

galvanometer  are  proportional  to  P ;  that  is  C  is  so  chosen  that  the  gal- 
vanometer deflection  is  reduced  to  one-half  that  observed  with  Cm-  If 
the  current  is  read  with  a  hot-wire  instrument  reading  directly  in  am- 
peres, then  the  reading  of  the  meter  corresponding  to  C  should  be  -— — 

of  that  corresponding  to  Cm,  since  1.41  =  V2.    This  expression  gives  the 

true  value  of  the  dampings  of  the  circuits  only  when  the  coupling  between 

them  is  extremely  loose. 

If  the  coupling  is  not  very  loose  between  the  two  circuits,  the  apparent 

value  of  the  damping  will  be  too  large.    The  proper  degree  of  coupling 

can  be  ascertained  by  observing  the  point  beyond  which  loosening  the 

coupling  does  not  decrease  the  damping.     If  the  damping  of  the  wave 

p 
meter  circuit  be  known  or  can  be  calculated  from  the  formula  80=  -^ — ^, 

by  subtracting  this  from  the  sum  of  the  two  dampings  we  get  at  once 
the  damping  of  the  other  circuit. 

If  we  wish  to  express  damping  in  terms  of  wave  length  A  instead  of 
capacity  or  inductance,  it  may  be  shown  mathematically  that  the  sum 

of  the  damping  8^  +  8^  =  Stt  ^^ — ^ ,  where  as  before  A  is  the  wave  length, 

which  reduces  the  square  of  the  received  current  to  one-half  of  that 
found  for  resonance  at  A,n.* 

239.  From  the  results  of  damping  measurements  it  has  been  found  that 
very  sharp  tuning  is  impracticable  when  a  wave  train  contains  less  than 
15  oscillations.  This  corresponds  to  a  decrement  of  .2  (fig.  18h).  Hav- 
ing measured  the  damping  of  the  open  circuit  as  coupled  and  found 
it  too  large,  it  is  necessary  to  add  inductance  in  order  to  decrease  it,  or  to 
weaken  the  coupling  in  order  that  the  total  resistance  R  may  be  decreased. 
If  it  is  not  practicable  to  change  the  wave  length,  the  aerial  must  be 
shortened  to  decrease  its  capacity  while  retaining  the  same  wave  length 
by  adding  inductance.  Loosening  the  coupling  also  decreases  the  damp- 
ing. 

Eeceiving  circuits  can  be  stiffened  without  changing  the  wave  length 
by  putting  a  condenser  in  series  to  decrease  the  capacity  and  then  add- 
ing inductance  to  keep  the  same  wave  length.  But  the  damping  of 
sending  circuits  can  not  be  conveniently  changed  in  this  way  on  account 
of  the  high  potentials  which  would  be  induced  in  the  series  condenser. 
The  method  of  measuring  damping  just  described  is  applicable  to  receiv- 
ing as  well  as  to  sending  circuits.  Eeceiving  circuits  have  In  general 
greater  high  frequency  resistance  than  sending  circuits,  but  specifications 

*  A  form  of  wave  meter,  specially  fitted  for  measuring  damping,  is  called 
a  "  decremeter."     Marconi  and  Kolster  decremeters  are  in  use. 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


203 


204  MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

require  that  their  decrement  shall  not  exceed  .3  for  any  wave  length  within 
the  range  of  the  set.  The  law  requires  that  the  decrement  of  transmitters 
shall  not  exceed  .2. 

MEASUREMENT  OF  SENDING  CURRENT. 

240.  For  measuring  the  sending  current  a  hot-wire  ammeter  is  installed 
directly  in  the  aerial  just  above  the  ground  connection.  Those  now  sup- 
plied are  graduated  to  read  directly  in  amperes. 

Curve  6,  fig.  Ill,  shows  hot  wire  ammeter  readings  in  open  circuit  for 
various  couplings  and  wave  lengths  at  the  Guantanamo  station.     The 

A-      '    t                ^'        f   1440-1120       oo^ 
maximum  reading  is  for  a  coupling  of    — t^^t^ =  *3^« 

The  highest  hot-wire  ammeter  reading  shows  that  the  circuits  are  in 
resonance  and  is  usually  taken  also  to  indicate  the  best  coupling;  but 
except  for  circuits  with  quenched  gaps  the  highest  H.  W.  A.  reading  is 
usually  obtained  with  a  coupling  which  causes  the  radiating  circuit  to  be 
too  highly  damped.  It  is  therefore  best  to  loosen  the  coupling  until  the 
shape  of  the  resonance  curves,  or  actual  measurements,  show  sufficiently 
small  damping;  and  then,  by  careful  adjustment  to  resonance,  attention 
to  connections,  to  spark  gap,  and  to  regulator,  get  the  highest  hot-wire 
ammeter  reading  that  can  be  obtained  with  that  coupling  and  wave  length. 

In  order  that  the  performance  of  different  sets  can  be  compared  it 
is  necessary  that  all  hot  wire  ammeters  be  calibrated  for  reading  directly 
and  correctly  in  amperes. 

A  hot  wire  ammeter  which  reads  correctly  on  direct  current  should 
be  calibrated  for  high  frequency  as  follows : 

First  remove  the  shunt  and  send  with  reduced  power  so  that  the  de- 
flections will  approximately  cover  the  scale.  This  can  be  done  either  by 
cutting  down  the  actual  power  or  by  loosening  the  coupling  between  the 
closed  circuit  and  aerial.  Note  the  deflections.  Then  close  the  shunt  and 
leaving  everything  else  unchanged,  send  again  and  note  the  deflection. 
The  relation  between  the  two  deflections  gives  the  ratio,  for  this  wave 
length,  of  the  shunted  to  the  unshunted  readings.  If  any  other  wave 
length  is  used,  the  shunt  must  be  recalibrated  since  its  effective  resistance 
depends  on  the  frequency. 

Eeports  of  current  in  aerial  should  always  read  correctly  in  amperes 
and  be  accompanied  by  report  of  exact  frequency  and  input  to  transformer 
in  amperes  and  volts.  It  is  found  that  the  distance  of  transmission  varies 
directly  as  the  oscillating  current  in  the  aerial,  so  that  it  is  important  to 
ascertain  correctly  what  this  current  is. 


manual  of  radio  telegraphy  and  telephony.  205 

the  shunted  telephone  method  of  measuring  the  intensity 
(loudness)  of  signals. 

241.  It  is  often  desirable  to  make  quantitative  determination  of  the 
intensity  of  incoming  signals,  especially  when  tests  are  being  made  of 
either  sending  or  receiving  apparatus.  This  can  be  done  if  the  station 
is  provided  with  an  electrolytic  receiver,  preferably  of  the  free-wire  type, 
and  a  resistance  box.    The  connections  are  shown  in  fig.  103. 


E> 


■E 


u 


K 


Fig.  117. — Detector  Circuit  with  Shunted  Telephone. 

Here  L  and  L^  are  wires  running  to  the  receiving  circuit,  K  a  stopping 
condenser,  D  the  electrolytic,  T  the  telephone,  R  a  resistance  box  in  shunt 
across  the  telephones,  P  the  potentiometer,  and  C  a  choke  coil  to  prevent 
the  oscillations  running  around  through  E  and  P  instead  of  passing 
through  D  when  the  shunt  R  is  closed.  Two  60-ohm  telephones  form  a 
suitable  choke.  Whatever  choke  coil  is  used,  it  should  be  tested  by  being 
placed  across  LL^.  If  the  choke  is  perfect  no  oscillations  will  pass 
through  it,  and  its  presence  across  LL^  will  not  diminish  the  loudness  of 
the  signals  in  the  telephones. 

The  measurement  of  the  intensity  of  signal  is  made  as  follows:  After 
the  receiving  circuit  and  detector  are  adjusted  to  give  maximum  loudness 
in  the  telephone,  the  shunt  resistance  R  is  closed  and  the  resistance  regu- 
lated until  the  signal  just  remains  audible.  The  value  of  the  current 
pulses  c  in  the  telephone,  which  are  proportional  to  the  energy  of  the 
incoming  waves  in  the  detector,  is  expressed  by  the  following  formula, 
vchere  r  is  the  value  of  the  shunt,  and  t  is  the  resistance  of  the  telephones, 
and  c*  the  least  current  audible  in  the  telephones : 

r-\-t    , 

c*  is  the  audibility  current,  and  the  signal  is  often  expressed  as  being 
80  many  times  audibility.  With  care  a  series  of  measurements  of  inten- 
sity may  be  made  to  agree  among  themselves  to  within  5  to  10  per  cent. 
Resistance  boxes  specially  made  up  and  calibrated  for  this  purpose  are 
called  "audibility  boxes." 

measurement  of  INDUCTANCE  AND  CAPACITY  AND  TOTAL  RESISTANCE. 

242.  Inductances  and  capacities  can  be  directly  measured  by  wave 
meters  as  follows: 


206  MANUAL    OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 

Inductance. — A  circuit  is  formed  containing  the  unknown  inductance, 
a  known  capacity  (one  or  more  standard  jars),  and  a  small  spark  gap. 
This  circuit  is  used  to  excite  the  wave  meter,  and  the  variable  condenser 
is  varied  until  a  maximum  current  in  the  wave  meter  is  obtained.  The 
two  circuits  being  then  in  resonance,  the  product  of  the  inductance  and 
capacity  in  each  is  the  same;  that  is,  LC  =  L^C^,  or  if  L  is  the  unknown 

quantity,  L=  —^. 

Capacity. — If  the  spark  circuit  is  made  up  with  a  known  inductance 

and  unknown  capacity,  by  the  same  process  we  determine  that  C=    ~^- . 

Li 

Total  Resistance. — This  expresses  all  the  losses  in  the  oscillating  circuit, 

and  is  determined  from  the  formula  previously  given  8  =   ^^  •    Having 

measured  8  and  L  and  found  n  the  frequency  from  the  wave  length,  we 
have  B  =  2nL8.  As  yet  we  have  no  standard  method  of  separating  R  into 
the  equivalent  radiation  resistance  and  true  high  frequency  resistance, 
which  are  its  principal  parts. 

THE  MEASUREMENT  OF  LOGARITHMIC  DECREMENT. 

Considering  the  Kolster  decremeter,  fig.  117b,  the  operation  for  measur- 
ing the  logarithmic  decrement  is  as  follows : 

The  rotary  condenser  is  first  set  at  the  position  of  complete  resonance  as 
indicated  by  the  maximum  deflection  of  the  sensitive  hot-wire  instrument, 
the  scale  readings  of  which  are  proportional  to  the  current  squared.  This 
maximum  deflection  is  now  reduced  to  one-half  its  value  by  decreasing  or 
increasing  the  capacity  of  the  rotary  condenser.  The  decrement  scale, 
which  may  be  rotated  independently,  is  now  set  at  zero,  then  clamped  so 
that  when  the  condenser  is  again  varied  it  will  rotate  with  it. 

Starting  at  the  zero  setting  of  the  decrement  scale  with  the  hot-wire 
instrument  reading  one-half  the  maximum  deflection,  the  condenser  is 
varied  continuously  in  one  direction  until  the  needle  of  the  hot-wire 
instrument  makes  a  complete  excursion  from  one-half  deflection  to  maxi- 
mum deflection  and  back  again  to  one-half  deflection.  The  scale  reading 
now  opposite  the  index  mark  0  is  the  value  of  S^-f  S,,  8i  being  the  decre- 
ment of  the  circuit  under  test  and  So  the  known  decrement  of  the 
instrument. 

It  will  be  noted  by  referring  to  fig.  117a  that  it  is  desirable  to  make  the 
zero  setting  of  the  decrement  scale  at  the  point  of  half  deflection  and  also  to 
take  the  final  reading  at  the  point  of  half  deflection,  because  at  these  points 
the  resonance  curve  is  steep,  and  consequently  the  settings  are  sharply 
defined  and  easily  made.  In  this  connection  it  will  be  noted  that  the 
formula 


MANUAL    OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 


207 


does  not  involve  the  resonant  value  of  capacity,  Cr,  but  only  those  at  the 
points  of  half  deflection  where  the  slope  of  the  resonance  curve  is  steep. 
This  formula  is  therefore  the  most  desirable  one  to  use,  and  the  decremeter 
is  consequently  operated  in  accordance  with  it. 

In  Fig.  117d  a  schematic  diagram  of  the  circuit  is  shown.  /  is  a  single- 
turn  coil  which  may  be  connected  in  the  circuit  under  test,  as,  for  example, 
the  aerial  circuit  of  a  radio  transmitter.    The  inductance  of  this  single 


Fig.  117a. — Kolster  Decremeter. 


turn  is,  in  the  majority  of  practical  cases,  small  as  compared  with  the  total 
inductance  of  the  circuit  under  test,  and  therefore  will  not  affect  the  tuning 
adjustment. 

The  coil  L  is  the  inductance  of  the  decremeter  circuit  and  is  so  arranged 
that  the  mutual  inductance  between  it  and  coil  I  can  be  easily  varied.  It  is 
very  essential  that  the  degree  of  coupling  between  the  circuit  under  test 
and  the  decremeter  circuit  be  small. 

Cv  is  the  variable  condenser  to  which  the  decrement  scale  is  attached 
through  gears.  In  parallel  with  Cv  is  a  small  condenser  Cf  which  remains 
fixed  in  value  after  proper  adjustment. 


208 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


H  represents  the  hot-wire  instrument  or  indicating  device,  the  scale  of 
which  is  so  marked  that  the  readings  are  proportional  to  the  square  of  the 
current  passing  through  it. 

A  crystal  dector  D  is  provided  and  the  wave  length  of  distant  stations 
may  be  measured  by  using  telephone  receivers  T. 


Fig.  117b. — Diagram  showing  relation  between  decrement  scale  and  resonance 

curve. 


By  means  of  a  switch,  the  buzzer  circuit  B  B  E  may  be  connected  to  the 
instrument  for  calibration  purposes. 

When  persistent  oscillations  of  single  frequency  are  emitted  from  a 
radio  transmitting  station  much  more  selective  receiving  apparatus  may 
be  employed  with  advantage  at  receiving  stations,  permitting  sharp  tuning 
with  consequent  minimizing  of  interference  caused  by  stations  other  than 
those  with  which  communication  is  desired. 


MANUAL   OP    RADIO    TELEGRAPHY    AND    TELEPHONY. 


209 


Since  the  logarithmic  decrement  is  a  measure  of  the  decay  of  a  train  of 
waves,  it  is  desirable  that  this  decrement  be  made  as  small  as  possible  in 


Fig.  117c. 


order  that  a  series  of  decaying  trains  of  waves  may  approach  as  near  as 
possible  to  the  condition  of  persistent  oscillations.    A  wave  train  having  a 


H 


Fig.  117d. — Diagram  of  connections. 

logarithmic  decrement  of  two-tenths,  the  limit  set  by  the  Federal  regula- 
tions, will  have  24  complete  oscillations  before  the  amplitude  of  the  last 
wave  has  decreased  to  1  per  cent  of  that  of  the  first. 
14 


Chapter  IX. 

CARE  AND  OPERATIOK. 

243.  At  all  stations,  ship  and  shore,  the  best  results  are  invariably 
obtained  and  the  most  satisfactory  service  given  by  alert  and  careful 
operators  who  take  pride  in  the  condition  of  their  instruments.  Eadio 
instruments  like  all  others  depend  for  their  efficiency  on  their  condition 
and  amply  repay  good  care.  Furthermore  a  neat  and  clean  outfit  inspires 
higher  efficiency  of  personnel. 

An  excellent  operator  once  said  that  no  matter  how  good  he  thought 
his  contacts  and  connections  were  he  always  found  that  by  going  over  them 
he  could  make  them  better  and  increase  his  sending  and  receiving 
efficiency.  A  routine,  which,  if  followed,  will  ensure  the  proper  care  of  a 
wireless  set,  is  given  in  Appendix  E. 

All  sliding  contacts,  especially  in  receiver  tuning  coils,  should  be  clean 
and  bright  and  free  from  foreign  matter.  Sending  key  contacts  should 
be  kept  clean  and  smooth  and  with  faces  parallel  to  each  other. 

Detectors  must  be  kept  in  their  most  sensitive  condition  and  frequently 
tested  by  means  of  the  buzzer  furnished  for  the  purpose.  When  using 
audion  detectors,  care  must  be  taken  not  to  use  too  much  battery  current 
which  would  shorten  the  life  of  the  bulb  or  burn  out  the  filament. 

When  any  part  of  the  condenser  is  injured  it  should  be  immediately 
replaced  or  repaired.  Any  change  in  closed  or  open  circuit  without  a 
corresponding  change  in  the  other  throws  the  two  circuits  out  of  reso- 
nance and  greatly  decreases  the  sending  radius. 

If  the  capacity  in  the  condenser  must  be  decreased  for  any  cause  then 
in  order  to  retain  the  same  wave  length  the  inductance  in  the  closed 
circuit  must  be  increased. 

244.  The  following  general  instructions  apply  to  all  stations:  The 
operator  shall  wear  the  double  head  receiver  continuously  while  on  watch, 
with  the  detector  adjusted  to  maximum  sensibility  and  tuner  adjusted  to 
proper  wave  length.  He  shall  satisfy  himself  by  frequent  testing  with  the 
buzzer  that  his  detector  is  sensitive,  and  while  in  the  vicinity  of  other 
vessels  or  near  shore  stations  and  using  a  detector  that  may  be  injured  by 
strong  sending,  he  shall  always  be  alert  to  protect  it  by  weakening  the 
coupling  or  by  opening  the  receiving  switch. 

In  order  to  avoid  interference,  he  shall  make  a  practice  of  loosening  the 
coupling  of  his  receiving  set  after  hearing  a  call  to  reduce  signals  to  a 
point  where  they  are  just  clearly  readable. 

He  shall  familiarize  himself  with  all  sending  and  receiving  connec- 
tions and  adjustments  and  be  able  to  tell  when  they  are  correct  and  to 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  211 

renew  them  when  necessary ;  but  he  shall  not  make  any  changes  in  any  of 
them  without  the  knowledge  and  permission  of  the  chief  electrician  or 
operator  in  charge. 

He  shall  be  capable  of  adjusting  the  spark  gap,  motor  and  generator 
rheostats  and  reactance  regulator,  so  as  to  obtain  the  necessary  output 
for  the  communication  to  be  made. 

He  shall  use  the  least  power  that  will  enable  his  messages  to  be  clearly 
read.  He  shall  be  vigilant  in  noting  and  keeping  in  good  condition  all 
sending  condenser  connections  and  in  keeping  all  articles  or  instruments 
which  might  be  injured  or  cause  a  ground  or  sparking  well  clear  of  the 
sending  apparatus  at  all  times. 

He  shall  not,  except  in  cases  of  emergency,  call  or  send  any  message, 
when  official  messages  are  being  sent  or  received  by  other  vessels  or 
stations  in  his  vicinity. 

He  shall  be  careful  to  file  correct  copies,  on  the  official  forms,  of  all 
messages  sent  and  received  by  him,  initialing  each  and  filling  in  time 
and  place  and  other  information  as  called  for  on  forms. 

He  shall  avoid  a  short  and  jerky  style  of  sending.  Dots  and  dashes 
and  intervals  must  be  of  proper  relative  lengths  as  shown  by  the  code  in 
order  that  the  sending  may  be  clear  and  legible.  Operators  must  en- 
deavor to  attain  fair  speed,  both  in  sending  and  receiving. 

Where  heavy  static  is  encountered,  dots  and  dashes  may  be  longer,  but 
must  preserve  their  relative  length.  The  generator  shall  be  run  only 
during  the  time  necessary  to  send  messages. 

Where  a  number  of  tunes  are  ordered  to  be  used  the  operators  shall  be 
careful  to  see  that  all  circuits  are  correctly  adjusted  before  attempting  to 
send. 

Each  operator  shall  turn  over  all  orders  to  his  relief  and  also  turn  over 
a  clean  and  neat  station. 

A  sending  set  with  all  connections  good,  closed  and  open  circuits  in 
resonance,  no  sparking  from  edge  of  condenser  jars  or  plates,  no  glow 
from  aerial  and  no  sparking  to  rigging,  is  utilizing  its  power  more 
efficiently  and  will  be  heard  farther  than  the  same  set  pushed  to  the  limit 
but  out  of  resonance  witli  high  resistance  connections  and  sparking  at  all 
points. 

jMessages  shall  not  be  sent  during  the  interval  in  which  naval  radio 
stations  send  the  time  signal  for  the  use  of  navigators  in  comparing 
chronometers  or  when  broadcasting. 

The  officer  or  electrician  in  charge  is  responsible  for  the  routine  of  the 
station  and  for  the  instruction  of  his  assistants  in  the  proper  use  of  the 
sending  and  receiving  apparatus  and  that  they  understand  and  carry  out 
all  orders.  He  should  stand  watch  sufficiently  to  keep  himself  expert  in 
sending  and  receiving  and,  in  any  case,  not  less  than  2  hours  daily. 


212  MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY. 

CALLING. 

245.  If  a  station  called  does  not  answer  the  call,  repeated  three  times 
at  intervals  of  2  minutes,  the  call  should  not  be  resumed  until  after  an 
interval  of  15  minutes,  the  station  making  the  call  having  first  made 
sure  that  no  other  communications  will  be  interfered  with. 

Repeated  and  continuous  calling  is  one  of  the  principal  sources  of  inter- 
ference. 

In  a  fleet,  when  a  ship  does  not  answer  after  a  first  call,  it  saves  time  and 
interference  to  shift  tune  rather  than  continue  to  call  on  the  first  tune 
used. 

This  does  not  apply  to  calling  merchant  ships  or  commercial  coast 
stations,  which  should  be  called  on  their  normal  wave  length. 

SENDING. 

246.  When  a  ship  is  within  ten  miles  of  another  which  is  receiving  faint 
signals,  the  first  ship  should  not  attempt  to  send  until  the  receiving  ship 
has  finished,  unless  she  sends  on  a  widely  different  wave  length  and  even 
then  she  should  not  use  more  than  1  kilowatt. 

Ships  in  the  same  vicinity  (within  20  miles)  should  not  use  more  than 
1  ampere  in  the  aerial  when  communicating. 

When  a  distress  signal  is  heard,  all  ships  and  stations  hearing  it  should 
at  once  cease  all  radio  work  and  not  attempt  to  communicate,  even  with 
the  vessel  in  distress,  unless  specially  requested  by  that  vessel  to  do  so. 

The  vessel  in  distress  should  make ,a  sufficient 

number  of  times  to  quiet  all  radio  work  and  should  follow  this  by  a 
broadcast  message  stating,  (1)  the  name  of  the  ship,  (2)  the  station  or 
ship  it  desires  to  communicate  with,  (3)  the  nature  of  her  distress,  (4) 
her  approximate  position,  (5)  by  a  general  call  (inquiry)  for  any  ship  or 
station  to  answer.  If  the  station  or  ship  called  by  the  vessel  in  distress 
does  not  answer,  the  General  Call  may  be  answered  by  anyone  within 
hearing.  As  soon  as  communication  with  the  vessel  in  distress  has  been 
established,  every  other  operator  should  preserve  absolute  silence.  When 
the  vessel  in  distress  has  finished  its  communications  her  operator  should 
send  a  broadcast  message  to  that  effect,  so  that  other  ships  may  go  ahead 
with  their  work  without  interfering. 

247.  The  sending  operator  should  not  attempt  to  attain  high  speed 
unless  he  knows  that  the  receiving  operator  is  fully  capable  of  receiving  at 
high  speed. 

Like  continuous  calling,  repetition  is  one  of  the  principal  sources  of 
interference. 

Steady  sending,  at  the  rate  of  about  20  words  per  minute,  will  give  the 
best  results. 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY.  213 

When  receiving  code  or  cipher,  an  operator  should  habitually  hand- 
print the  letters  rather  than  write  them  in  the  ordinary  long  hand.  If 
this  is  done  fewer  mistakes  will  occur  in  decoding  or  in  repeating  a 
message,  especially  if  the  decoding  or  repeating  of  a  message  is  done  by 
an  operator  other  than  the  one  who  did  the  receiving,  due  to  the  difficulty 
of  the  latter  reading  the  former's  handwriting.  This  is  especially  true 
of  the  letters  n  and  u,  u  and  v,  m  and  w,  z  and  g,  and  a  and  o,  which 
are  often  misread  for  one  another  in  ordinary  handwriting.  The  fact 
that  code  words  are  once  repeated  allows  the  receiving  operator  time  to 
take  this  extra  precaution. 

Code  and  cipher  should  be  sent  at  a  speed  about  one-third  slower  than 
plain  language  and  great  care  should  be  taken  to  leave  an  appreciable 
space  between  the  groups  of  letters  and  the  interval  character  separating 
these  groups,  otherwise  the  interval  character  is  apt  to  be  confused  as  part 
of  a  code  group. 

When  hand-printing,  the  letters  0  and  D  should  be  made  carefully, 
lest  the  operator  make  a  D  which  will  be  read  as  an  0,  or  vice  versa,  and 
similarly  for  the  letters  G  and  Q,  U  and  V,  and  V  and  Y.  Operators 
should  frequently  practice  rapid  hand-printing  in  order  that  they  may 
become  expert. 

Special  care  should  be  taken  with  the  address  and  signature. 

DUPLEX   OPERATION. 

247a.  A  high-powered  sending  set  can  be  operated  continuously  for 
sending  if  the  receiving  for  the  same  station  is  done  on  a  different 
antenna  at  a  distant  point  (several  miles  away),  in  order  that  the  sending 
will  not  interfere  with  the  receiving  done  simultaneously  on  a  slightly 
different  wave.  In  such  a  case  the  operator  at  the  receiving  station  uses  a 
small  sending  key  connected  electrically  with  a  relay  at  the  sending  station, 
which  operates  a  solenoid  whose  armature  carries  a  lever  which  acts  as  the 
sending  key  for  the  main  sending  set.  A  sending  station  operating  by 
distant  control  from  a  near-by  operating  station  in  this  manner  generally 
carries  on  what  is  known  in  radio  as  "duplex"  operation  with  a  siuiilar 
station,  such  that  both  stations  are  continuously  sending  to  one  another. 

HIGH-SPEED  OPEEATIOX. 

247b.  High-powered  stations,  carrying  on  continuous  conminnication 
with  one  another,  are  sometimes  equipped  with  apparatus  such  that  the 
sending  and  receiving  is  done  automatically,  at  speeds  up  to  about  150 
words  per  minute. 

To  accomplish  this  the  sending-key  solenoid  is  operated  electrically 
by  means  of  a  current  controlled  by  a  make  and  break  contact  maker  which, 


214  MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPPIONY. 

in  turn,  is  controlled  by  perforations  of  dots  and  dashes  on  tape,  which 
latter  is  fed  through  a  Morse  writer;  the  dots  and  dashes  being  previously 
punched  in  the  tape  in  the  same  manner  as  is  done  for  cable  operation. 

To  keep  the  contacts  of  high-speed  sending  keys  cool,  and  to  prevent 
arcing  across  these  contacts,  a  jet  of  cold  air  under  pressure  is  played  on 
the  contacts. 

The  receiving  of  high-speed  signals  is  done  by  means  of  a  phonograph, 
on  the  record  of  which  the  signals  "  talk."  After  the  signals  are  recorded 
on  a  record  the  latter  is  run  at  a  slow  speed  such  that  it  repeats  the  signals 
to  an  operator  at  a  speed  such  that  the  signals  can  be  read. 

248.  TO  SEND  A  MESSAGE 

Example. — Ship  Prairie  (NQM)  calls  coast  station  Key  West  (NAR): 
NAR  acknowledges  call:  NQM  sends  message:  NAR  acknowledges  receipt: 
Qnish. 

Call. 

1.  m  0  ^H  %  m   Attention  signal. 

2.  NAR    NAR     NAR Station  called. 

3.  ^  •  •     •   De. 

4.  NQM     NQM     NQM Calling   station. 

Reply, 

5.  Bi  ^  m  %  ^H   Attention  signal. 

6.  NQM     NQM     NQM  Calling   station. 

7.  Hi  •  •    •   De. 

8.  NAR Acknowledging    station. 

9.  g_  0  BB   Go  ahead. 

Message. 

10.  ■■  %  m  #  IB    Attention  signal. 

11.  Alert    Office  of  origin. 

12.  5    Number  of  radiogram. 

13.  XN    Sending  operator's  sign. 

14.  7    Check. 

15.  Twelfth    Original  date  of  message. 

16    ■■  •  •  •  WM     Break. 

17.  Govt.  Secnav  Washington  Address. 

18.  ■■  •  •  •  ■■    Break 

19.  Apache  Mazanilla  Phalara Text. 

20.  ■■  •  •  •  WM     Break. 

21.  Alert    Signature. 

22.  #  ■■  #  ■■  •    End  of  message 

23.  NQM  Call  letters  of  sending  station. 

24.  ^m  •  WM   Go  ahead. 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  215 

Acknowledgment. 

25.  NQM  Station  which  sent  message. 

26.  #  ■■  #  Received. 

27.  5    No.  of  message. 

28.  NAR  Receiving  station. 

29.  SP Receiving  operator's  sign. 

30.  ■■  •  ■■    Go  ahead. 

Finished  Signal. 

31.  •  •  •  WU  •  ■■    Finished. 

32.  NQM Sending  station. 

RECEIVING. 

249.  In  ordinary  circumstances,  while  listening  in,  the  set  may  be  kept 
closely-coupled,  to  broaden  the  tune ;  but  the  aerial  circuit  should  be  stiff, 
i.  e.,  having  a  considerable  amount  of  inductance  (art.  231).  The  aerial 
circuit  should  be  tuned  with  a  variable  condenser  in  series  for  short  waves 
and  in  parallel  (around  inductance)  for  long  waves  (fig.  92). 

When  the  calling  station  is  well  tuned  in,  loosen  the  coupling,  if  there 
is  interference.  This  should  be  done  gradually,  adjusting  both  the  open 
(aerial)  and  closed  circuits  with  each  change  of  coupling,  until  a  point  is 
reached  where  signals  are  readable  through  the  disturbances.  With  fairly 
strong  signals  the  coupling  on  a  1  P.  76  receiver  should  be  not  less  than  16 
on  the  coupling  scale,  and,  at  this  point,  for  moderate  wave  lengths,  the 
signal  should  not  fall  materially  in  intensity. 

For  further  improvements  in  tuning,  the  closed  circuit  condenser  should 
be  made  as  large  as  possible  and  the  closed  circuit  inductance  correspond- 
ingly reduced. 

The  settings  (for  best  coupling  and  of  open  and  closed  circuits)  for  all 
stations  habitually  communicated  with  should  be  recorded  and  posted  for 
the  use  of  the  operator  on  watch. 

The  practice  of  loosening  coupling  while  receiving  should  be  made 
obligatory  on  all  operators.  It  not  only  cuts  out  existing  interference,  but 
prepares  for  any  interference  which  may  arise  during  reception.  Owing 
to  the  change  of  effective  self-induction,  in  both  circuits,  both  require 
readjustment  (retuning)  with  each  change  of  coupling. 

Two  aerials  in  the  same  immediate  vicinity  as  on  board  the  same  ship 
have  an  influence  on  each  other  so  that  if  both  are  used  for  receiving  at 
the  same  time,  the  tuning  of  either  will  affect  the  other  and  this  effect 
may  be  observed  between  aerials  on  different  ships  if  they  are  very  close 
together. 

250.  When  two  ships  are  close  together,  the  one  which  is  not  doing  the 
sending  can  generally  assist  in  receiving  faint  signals.  Eegardless  of 
opening  of  circuits,  high  power  sending  lessens  the  sensitiveness  of  the 


216  MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 

detector  of  the  sendintr  station  when,  as  usual,  the  transmitter  and 
detector  are  only  a  few  feet  apart.  Quite  frequently  in  the  tropics,  it 
occurs  that  signals  "  swing  "  in  and  out  (par.  175) ;  that  is,  they  are  easily 
readable  for  a  few  seconds,  and  a  few  seconds  later  become  hardly  audible, 
and  alternately  grow  strong  and  weak  in  this  manner.  Sometimes  this 
can  be  overcome  by  a  slight  shift  of  wave  length,  but  more  often  by  allow- 
ing the  spark  gap  frequent  cooling  periods.  After  once  establishing 
communication,  under  such  conditions,  do  not  call  again  unnecessarily, 
but  commence  at  once  with  the  message,  otherwise  the  gap  will  heat  up 
before  the  message  is  well  underway.  It  is  often  advisable  to  pause  after, 
say,  every  10  words,  under  such  conditions,  to  listen  for  the  receiving 
operator's  OK,  otherwise  many  repetitions  may  be  required ;  these  pauses 
also  assist  in  keeping  the  gap  cool. 

INTERFERENCE. 

251.  The  foregoing  articles  indicate  specifically  how  to  avoid  interfer- 
ing with  others  and  how  to  work  through  interference,  but  additional  con- 
certed methods  must  be  employed  to  avoid  interference  other  than  static. 

The  mere  establishment  of  standard  wave  lengths  promotes  interference, 
in  one  sense,  since  it  ensures  that  there  will  be  stations,  ship  and  shore,  in 
the  same  vicinity,  wishing  to  communicate  at  the  same  time  on  the  same 
wave  length,  but  it  conduces  to  safety.  As  between  ship  and  shore  stations, 
the  latter  controls  and  decides  upon  the  order  in  which  she  will  take  and 
send  (clear)  messages. 

As  between  two  shore  stations  ia  adjacent  countries,  or  the  same 
country,  both  having  business  with  ships,  or  between  men-of-war  of  dif- 
ferent nationalities,  a  division  of  time  is  arranged. 

For  shore  stations  communicating  only  with  other  shore  stations,  specific 
tunes  (wave  lengths),  widely  different  from  the  standard,  are  assigned. 

As  between  merchant  ships  in  the  same  vicinity  and  merchant  ships  and 
men-of-war,  mutual  forbearance  and  patience  are  absolutely  necessary. 

It  is  often  of  value,  in  working  through  interference,  to  reduce  the  fre- 
quency of  the  note  by  reducing  the  speed  of  the  motor  generator  below 
normal.  This  is  especially  valuable  when  several  sets  are  operating  in  the 
same  general  vicinity. 

Shifting  the  sending  coupling  is  another  thing  which  will  sometimes 
give  the  receiving  operator  a  better  opportunity  to  receive  through  inter- 
ference. In  the  latter  case  the  antenna  inductance  must  be  re-adjusted 
to  give  maximum  radiation. 

In  fleets,  standard  calling  tunes  are  established  and  a  wide  range  of 
wave  lengths  (differing  by  a  percentage  sufficient  to  avoid  interference  iu 
ordinary  circumstances)  are  assigned  for  communicating ;  these  times  are 
known  by  their  letters,  as  A,  B,  C,  etc. 


MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY.  217 

The  vessel  called,  when  she  acknowledges  the  call,  designates  the  com- 
municating tune  as  C  or  D  to  be  used  by  the  sending  vessel,  so  as  to  avoid 
interference  with  other  tunes  audible  in  the  receiver  of  the  vessel  called. 

If  two  operators  "  lose  "  one  another  in  an  attempt  to  shift  to  a  different 
tune  to  avoid  interference,  both  should  return  to  the  original  tune,  and 
thus  avoid  delay  and  confusion. 

It  should  be  borne  in  mind  in  this  connection  that,  although  any  one 
of  a  wide  range  of  wave  lengths  may  be  selected,  the  waves  close  to  the 
fundamental  carry  much  greater  distances  than  do  the  extreme  wave 
lengths. 

When  all  sending  and  receiving  sets  on  all  ships  are  calibrated  and  con- 
structed so  as  to  permit  easy,  rapid  and  definite  changes  of  wave  length, 
while  remaining  properly  coupled,  calling  and  communicating  tunes 
might  be  established  and  designated  by  international  agreement  and 
assist  in  relieving  the  existing  congestion. 

STATIC. 

252.  The  use  of  undamped  oscillations  will  materially  assist  in  the 
sharp  tuning  necessary  to  prevent  interference  by  the  use  of  standard 
calling  wave  lengths  and  codified  standard  communicating  wave  lengths ; 
but  neither  undamped  nor  damped  oscillations  can  be  relied  upon  to  com- 
pletely eliminate  the  effects  of  the  vagrant  waves  and  local  electrification 
grouped  under  the  name  of  "  static." 

Every  lightning  discharge  produces  powerful  electric  waves  which 
affect  conductors  at  great  distances,  and  since  thunderstorms  in  warm 
climates,  and  especially  in  summer,  are  almost  continuous  in  the  sense 
of  existing  somewhere  in  the  area  in  which  they  affect  detectors,  the 
interference  caused  by  them  is  almost  continuous. 

The  waves  created  by  lightning  discharges  vary  greatly  in  length ;  but 
are  highly  damped  and  affect  all  aerials  more  or  less.  Again,  at  every 
wireless  station  the  air  at  the  top  and  foot  of  the  aerial  is  at  different 
potentials.  The  atmospheric  potential  gradient  at  any  station  varies 
with  the  time  of  day,  the  season  of  the  year,  and  the  local  weather  con- 
ditions.    It  is  usually  steeper  in  summer. 

This  difference  of  potential  tends  to  equalize  itself  through  the  aerial. 

The  upper  air  is  usually  positively  electrified,  the  earth  negatively. 

The  amount  and  regularity  of  the  discharge  to  ground  at  any  time 
depend  on  the  difference  of  potential  between  the  upper  air  and  the 
ground  at  the  time  and  the  amount  of  electrified  air  which  comes  in 
contact  with  the  aerial. 

The  discharges  are  usually  intermittent  and  vary  in  strength.  Some- 
times they  produce  a  continuous  roar  in  the  telephone. 

In  this  respect  the  note  of  the  spark  affects  reception  and  it  is  possible 
to  read  a  500-cycle  note  through  static  which  would  render  a  60-cycle 


218  •    MANUAL    OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 

note  unintelligible.  As  previously  stated,  the  use  of  the  heterodyne  per- 
mits the  note  of  received  signals  to  be  controlled  at  will. 

Whatever  tends  to  selectivity  or  inertia  in  receiving  circuits,  such  as 
large  inductances,  also  tends  to  decrease  static  interference. 

Inductively  coupled  receiving  sets  afford  a  direct  path  to  ground,  so 
that  static  charges  do  not  accumulate  on  the  aerial,  and  the  inductive 
coupling  weakens  the  energy  transfer  of  all  induced  currents  which  are 
out  of  tune. 

A  silicon  detector,  connecting  the  aerial  to  ground  above  the  receiving 
inductance,  has  been  used  with  fair  success  at  Key  West  for  cutting  out 
static* 

We  see  that  loose  coupling,  small  damping  and  high  frequency,  which 
we  desire  for  other  reasons,  are  also  desirable  as  tending  to  eliminate 
static  interference.f 

CODES. 

253.  Prior  to  July  1,  1913,  the  date  set  for  putting  the  London  conven- 
tion into  effect,  commercial  shore  stations  in  the  United  States,  and 
United  States  coasting  vessels  used  American  Morse. 

All  foreign  stations,  ship  and  shore,  public  and  private,  used  Conti- 
nental Morse.  American  Morse  is  a  little  faster.  The  Continental  Morse 
is  a  dash  and  dot  code  throughout  with  a  maximum  of  four  elements  in 
any  letter.  The  American  Morse  uses  five  elements  in  the  letter  P,  four 
elements  and  a  space  in  Y,  Z  and  &,  and  a  long  dash  for  the  letter  L.  It 
has  a  relatively  less  number  of  dashes  than  the  Continental  code  and  is  on 
that  account  faster. 

A,  B,  D,  E,  G,  II,  I,  K,  M,  N,  S,  T,  U,  V  and  W  (fifteen  out  of  the 
twenty-six  letters  of  the  alphabet)  are  the  same  in  both  codes. 

It  is  to  be  hoped  that  the  use  of  wireless  telegraphy  will  eventually 
bring  about  an  international  agreement  as  to  the  elements  for  the  re- 
maining eleven  letters  and  thus  provide  a  universal  code  ashore  and  afloat. 

When  it  is  desired  to  communicate  by  the  international  signal  book  (as 
between  two  vessels  whose  operators  do  not  use  the  same  language)  the 
"  call "  should  be  followed  by  the  letters  P  R  B  in  the  Continental  code 
(art.  255). 

It  is  important  that  operators  aboard  ship  learn,  and  become  expert 
in,  the  American  Morse  code,  since  they  must  use  this  code  at  shore 
stations  in  handling  land  wires. 

*  This  method  of  cutting  out  static  is  proposed  by  Dr.  Austin. 

t  The  British  Association  for  the  Advancement  of  Science  has  undertaken  a 
systematic  investigation  of  the  phenomena  grouped  under  the  head  of  "  static." 
It  states  that  as  far  as  is  yet  known  the  natural  electric  waves  reaching  wireless 
telegraph  stations  in  latitudes  above  50°  north  appear  to  travel  mostly  from 
the  south. 


MANUAL   OF    KADIO    TELEGRAPHY   AND   TELEPHONY.     '  219 


The  international  signal  of  distress  is  •  •  •  ■■  ■■  ■i  •  •  •  > 
making  the  letters  S  0  S  of  the  Continental  code  (appendix  C). 

The  two  signals  given  above  were  adopted  nt  the  International  Wire- 
less Telegraph  Conference  at  Berlin  in  IDOG. 

254.  INTERNATIONAL   MORSE   CODE   SIGNALS. 

(To  be  used  exclusively  for  all  radio  communications.) 

Spacing  and  Length  of  Signals. 

1.  A  dash  is  equal  to  3  dots.  3.  The  space  between  two  letters  is 

2.  The    space    between    the    signals  equal  to  3  dots. 

which   form    the  same   letter   is      4.  The  space  between   two  words   is 
equal  to  one  dot.  equal  to  5  dots. 


LETTERS. 

A 

#  1^ 

U       •  •  ^ 

B 

■i  •  •  • 

V       •  •  •  ^ 

C 

WM  •  WM  • 

W       •  ■■  Hi 

D 

IB  •  • 

X       WM  •  •  1^ 

E 

• 

Y       WM  •  WM  Hi 

F 

•  •  ■■  • 

Z      WM  ^M  •  • 

G 

■■  ■■  • 

a  (German) 

H 

•  •  •  • 

•  WM  •  H 

I 

•  • 

a  or  a  (Spanish-Scandinavian) 

J 

•  ■■  ■■  §■ 

•  ^M  ■■  •  ■■ 

K 

^M  •  ^m 

ch   (German) 

L 

•  ^  •  • 

■i  ■■  ■■  Hi 

M 

^m  WM 

6  (French) 

N 

tm  • 

•  •§■•• 

0 

■1  IH  ^M 

n   (Spanish) 

P 

•  ^M  WM  • 

■1  ^M  •  ■■  ^m 

Q 

■1  ^M  •  ■■ 

6  (German) 

R 

•  ^  • 

■■  ■■  ■■  • 

S 

•  •  • 

ii  (German) 

T 

"" 

NUMERALS. 

1 

•  ■■  IB  Hi  ■! 

6         ^  •  •  •  • 

2 

^  ^  •  •  • 

3 

•  •  •  ■■  Bl 

■1  ^M  ^M  •  • 

4 

•  •••■■ 

■■  1^  ■■  ■■  4 

5 

■1  ■■  m  ^  ■ 

PUNCTUATION   AND  OTHER  SIGNS 

Full  stop   (.)    ••     •#     ## 

Semicolon    ( ; )    WM  #  ^H  #  WM  # 

Comma   (,)    •■■•■§•■■ 

Colon (:)    ^^■■••9 


220  MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 


Interrogation  or  REPEAT (?)  •  •  tm  ■■  •  • 

Exclamation   (!)  ^M  ■■  #  #  ■■  ■■ 

Apostrophe    (')  #  ■■  MM  !■  j^l  • 

Hyphen  or  dash (-)  Hi  •  •  •  •  HI 

Bar  indicating  fraction (/)  Bi  #  #  ■■  # 

Parenthesis  (before  and  after  words) (  )  ■■  •  ^M  ■■  #  ■■ 

Quotation  marks  (before  and  after  each  word 

or  each  passage  quoted) ("  ")  #  ■■  #  #  ■■  # 

Underline  (before  and  after  words  or  part  of 

phrase)    ( — )  •  •  ■■  ^B  •  ^M 

ATTENTION   (or  call) WM  •  ■■  •  IB 

Double  dash  or  BREAK   (signal  separating 

preamble  from  address,  address  from  text, 

and  text  from  signature) (=)  ■■  •  •  •  ■■ 

UNDERSTOOD •  •  •  WM  • 

ERROR •  •  •  •  •  •  #  • 

GO  AHEAD IH  •  ^ 

END  OF  MESSAGE •  ■■  •  ^  • 

WAIT    •  ^  •  •  • 

RECEIVED    (acknowledgment  of  receipt  of 

message)    #  ■■  • 

FINISHED  (end  of  work)   •••■^•liB 

In  official  repetitions  and  in  the  preamble  of  radiograms,  figures  may  be 
rendered  by  means  of  the  following  signals,  which  may  also  be  used  in  the  text 
of  telegrams  containing  figures  only.  Radiograms  must,  in  this  case,  bear  the 
service  instructions  "  in  figures." 


2««H1  1  mM  •  •  9 

With  the  adherence  of  the  United  States  to  the  Berlin  Convention, 
which  requires  all  commercial  ships  flying  our  flag  to  use  the  International 
code,  and  the  adoption  of  that  code  for  communication  between  the  army 
and  navy,  the  necessity  for  using  the  American  Morse  code  for  any  purpose 
except  land  line  telegraphy  has  been  eliminated.  The  International  Morse 
code,  alphabet,  numerals,  punctuation,  etc.,  shall  be  used  exclusively  for 
all  radio  communications.  In  addition  to  the  letters  of  the  English  alpha- 
bet, the  following  foreign  letters  may  be  used  by  ships : 


a  (German)  #  ■■  •  ^B 
d  or  a,  (Spanish-Scandinavian)         #  ■■  Hi  #  ■ 

ch   (German)  ■■  ■■  WM  ■ 

6  (Spanish)  #  #  ■■  •  # 

fi  (Spanish)  MM  ■■  •  ■■ 

0  (German)  IB  ■■  IH  # 

u  (German)  #  #  Bi  Hi 


MANUAL   OF   RADIO    TELEGRAPHY   AND   TELEPHONY.  221 

AMERICAN  MORSE  CODE  USED  BY  LAND-LINE  COMPANIES. 


A 

#  WM 

J 

■■  •  ■■  • 

s   •  •  • 

B 

^  •  •  • 

K 

■■  •  WM 

T     ^ 

C 

•  • 

• 

L 

■■i 

u   •  •  ■■ 

D 

■1  # 

• 

M 

■i  ■■ 

V     •  •  •  Bi 

E 

N 

^m  • 

W    •  ^  IB 

F 

#  ■■ 

• 

0 

•  • 

X    •  ■■  •  « 

G 

■■  ■ 

■  • 

P 

•  •  •  •• 

Y     •  •     •  • 

H 

•  •  •  • 

Q 

•  •  Hi  • 

z    •  •  •   • 

I 

•  • 

R 

•    •  • 

1 
2 

•  •  ■ 

■  • 

• 
• 

NUMERALS. 

6 

7 

A  t 

k   A   A   A   A 

w  f 

P   V   V   V  V 

3 

•  •  • 

■■ 

• 

8 

■i 

•   •   •   • 

4 

•  •  • 

•  1 

■i 

9 

■1 

•  •  Hi 

5 

fH  ■ 

1  ■ 

1 

0 

^H 

PUNCTUATION  AND  OTHER  SIGNS. 

Full  Stop    (.)     •  •  Bi  ^M  •  • 

Semicolon    (;)     •••     •• 

Comma     ( , )     •  ■■  •  ■■ 

Interrogation   or   repeat (?)     HH  •  •  IHI  • 

Exclamation    (!)     ■■  ■■  ■■  # 

Beginning  of  bracket ([)     •  •  •  •  •     ■■  # 

Ending  of  bracket (])     #####     ##    ## 

Hyphen  or  dash (-)     ••••     •^•^ 

Dollar  mark   ($)     •••    •■■•• 

Quotation    ("  ")     9  #  ^M  #     ■■  # 

HAVE  YOU  ANYTHING  FOR  ME? ■■  1^  ^ 

I  AM  BUSY IH  •  •  •  • 

ABBREVIATIONS. 

255.  The  following  abbreviated  signals  will  go  into  effect  with  the 
London  Convention,  July  1^  1913,  and  will  be  used  by  ships  of  all  nations 
which  may  ratify  that  convention. 

■i  •  H  #      ■■  ■■  #  ^M     (CQ)     Signal  of  inquiry,  or  General  Call, 

made    by    a    station    desiring    to 

communicate. 
■■      #  ■■  #     (TR)  Signal  preceding  position  report;  or 

"  Send  position  report." 
■■  ■■  •  •  ^M  ^M     (!)  Signal  indicating  that  a  station  is 

about  to  send  at  high  power. 


232 


\ 


MANUAL    OF   RADIO    TELEGRAPHY    AND   TELEPHONY, 


Abbre- 
via- 
tion. 


Question. 


Answer  or  notice. 


PRB 

QRA 
QRB 
QRC 
QRD 
QRF 
QRG 
QRH 
QRJ 
QRK 
QRL 


QRM 
QRN 
QRO 
QRP 
QRQ 
QRS 
QRT 
QRU 
QRV 
QRW 

QRX 
QRY 
QRZ 
QSA 
QSB 

QSC 
QSD 
QSF 

QSG 
QSH 
QSJ 
QSK 
QSL 
QSM 
QSN 
QSO 

QSP 
QSQ 
QSR 
QST 
QSU 

QSV 

QSW 
QSY 
QSX 


Do  you  wish  to  communicate  by  means  of  the 

International  Signal  Code? 
What  ship  or  coast  station  is  that  ? 
What  is  your  distance  ? 
What  is  your  true  bearing  ? 
Where  are  you  bound  for  1 
Where  are  you  bound  from? 
What  line  do  you  belong  to  ? 
What  is  your  wave  length  in  meters? 
How  many  words  have  you  to  send  ? 
How  do  you  receive  me? 
Are  you  receiving  badly?  Shall  I  send  20 

•   ••■■• 

for  adjustment  ? 
Are  you  being  interfered  with? 
Have  you  much  static  ? 
Shall  I  increase  power  ? 
Shall  I  decrease  power  ? 
Shall  I  send  faster? 
Shall  I  send  slower? 
Shall  I  stop  sending? 
Have  you  anything  for  me  ? 
Are  you  ready? 
Are  you  busy  ? 

Shall  I  stand  by? 
When  will  be  my  turn  ? 
Are  my  signals  weak  ? 
Are  my  signals  strong  ? 
Is  my  tone  bad  ? 
Is  my  spark  bad  ? 
Is  my  spacing  bad  ? 
What  is  your  time  ? 

Is  transmission  to  be  in  alternate  order  or  in 
series  ? 

What  rate  shall  I  collect  for ? 

Is  the  last  radiogram  canceled  ? 

Did  you  get  my  receipt  ? 

What  is  your  true  course  ? 

Are  you  in  communication  with  land  ? 

Are  you  in  communication  with  any  ship  or 

station  (or,  with )? 

Shall  I  inform that  you  are  calling  him? 

Is calling  me? 

Will  you  forward  the  radiogram  ? 

Have  you  received  the  general  call  ? 

Please  call  me  when  you  have  finished  (or) 

at o'clock. 

Is  public  correspondence'  being  handled  ? 

Shall  I  increase  my  spark  frequency? 

Shall  I  send  on  a  wave  length  of meters  ? 

Shall  I  decrease  my  spark  frequency? 


I  wish  to  communicate  by  means  of  the  Inter- 
national Signal  Code. 

This  is 

My  distance  is 

My  true  bearing  is degrees. 

I  am  bound  for 

I  am  bound  from 

I  belong  to  the Line. 

My  wave  length  is meters. 

I  have words  to  send. 

I  am  receiving  well. 

I  am  receiving  badly.     Please  send  20 

•  •  •  Hi  • 

for  adjustment 
I  am  being  interfered  with. 
There  is  much  static. 
Increase  power. 
Decrease  power. 
Send  faster. 
Send  slower. 
Stop  sending. 
I  have  nothing"for  you. 
I  am  ready.     All  right  now. 

I  am  busy  (or  :  I  am  busy  with ).  Please 

do  not  interfere. 
Stand  by.    I  will  call  you  when  required. 

Your  turn  will  be  No 

Your  signals  are  weak. 
Your  signals  are  strong. 
Your  tone  is  bad. 
Y'our  spark  is  bad. 
Y'our  spacing  is  bad. 

My  time  is 

Transmission  will  be  in  alternate  order. 

Transmission  will  be  in  series  of  5  messages. 
Transmission  will  be  in  series  of  10  messages 

Collect for 

The  last  radiogram  is  canceled. 
Please  acknowledge. 

My  true  course  is degrees. 

I  am  not  in  communication  with  land. 

I   am  in  communication  with (through 

) 

Inform that  I  am  calling  him. 

You  are  being  called  by 

I  will  forward  the  radiogram. 
General  call  to  all  stations. 
Will  call  when  I  have  finished. 

Public    correspondence'    is    being    handled. 

Please  do  not  interfere. 
Increase  your  spark  frequency. 

Let  us  change  to  the  wave  length  of meters. 

Decrease  your  spark  frequency. 


'Public  correspondence  is  any  radio  work  handled  on  the  commercial  tunes  300  or  600. 

Ad(iitional  abbreviation  proposed  for  international  use,  and  authorized 
for  naval  stations: 


Abbre- 
via- 
tion. 

Question. 

Answer  or  notice. 

QSZ 

Send  each  word  twice.    I  have  difficulty  in 
receiving  you. 

When  an  abbreviation  is  followed  by  a  mark  of  interrogation,  it  refers 
to  the  question  indicated  for  that  abbreviation. 


MANUAL   OF    RADIO    TELEGRAPHY    AND   TELEPHONY.  223 

EXAMPLES. 

Station  A.  QRA?  =Wliat  is  the  name  of  your  ship  or  station? 

Station  B.    QEA  Celtic  MLC  =This  is  the  Celtic.    Her  call  is  MLC. 
Station  A.  QRG?  =To  what  line  do  you  belong? 

Station  B.  QRG  White  Star  =1  belong  to  the  White  Star  line? 
QRZ  =Your  signals  are  weak. 

Station  A  then  increases  the  power  of  its  transmitter  and  sends : 
Station  A.  QRK?  =How  are  you  receiving? 

Station  B.  QRK  =1  am  receiving  well. 

QRB  80  =My  distance  is  80  nautical  miles. 

QRC  62  =My  true  bearing  is  62  degrees,  etc. 

COMMERCIAL  OPERATION  BY  UNITED  STATES  NAVAL  COMMUNICATION 

SERVICE. 

By  an  Act  of  Congress,  approved  August  13,  1912,  entitled,  "  An  Act  to 
Regulate  Radio  Communication,"  the  Secretary  of  the  Navy  was  directed 
to  open  certain  naval  radio  stations  to  general  public  service.  This  service 
involves  the  handling  of  commercial  traffic  to  and  from  all  ships  at  sea,  and 
between  certain  fixed  points  on  shore. 

The  term  "  commercial,"  as  applied  to  radiograms,  is  used  to  denote  all 
messages  other  than  of  official  nature.  In  addition  to  the  coastal  stations 
open  to  this  service,  all  vessels  of  the  navy  are  directed  to  handle  com- 
mercial traffic  for  convenience  of  the  officers,  crew  and  the  public. 
Arrangements  have  been  made  Avith  the  principal  land  line  and  cable  com- 
panies, as  well  as  the  radio  operating  companies,  for  the  interchanging 
of  this  traffic,  so  that  whether  it  be  land  or  sea,  all  telegraph  facilities  are 
linked  with  the  Naval  Communication  Service. 

These  arrangements  include  the  handling  of  commercial  traffic  in  and 
with  Alaska.  During  interruptions  to  the  Army  Cable  System,  the  work 
is  taken  up  by  the  radio  circuit.  In  the  United  States,  during  interruptions 
to  the  land  line  service,  the  Naval  Communication  Service  fills  in  the 
breaks,  carrying  the  traffic  across  these  breaks  and  acting  as  an  adjunct  to 
the  telegraph  service  when  all  other  means  of  communication  fail. 

The  accounting  in  connection  with  the  handling  of  commercial  traffic  is 
centralized  into  the  office  of  the  Director  Naval  Communications,  and 
through  this  service  the  traffic  is  carefully  checked  and  payments  made  by 
that  office  to  the  connecting  lines. 

SOURCES  OF   INFORMATION. 

256.  The  act  regulating  apparatus  and  operators  on  merchant  steamers, 
which  has  been  in  effect  since  July  1, 1911,  will  be  found  in  Appendix  D. 

The  act  regulating  licenses,  wave  lengths,  decrement,  etc.,  and  author- 
izing the  Secretary  of  the  Navy  to  open  certain  naval  wireless  stations  to 


224  MANUAL   OF    RADIO    TELEGRAPHY   AND   TELEPHONY. 

commercial  business  and  to  fix  rates  for  this  service,  will  also  be  found  in 
Appendix  D.    This  act  went  into  effect  December  13, 1912. 

The  most  important  rules  of  the  London  Convention,  which  went  into 
effect  on  July  1,  1913,  will  be  found  in  Appendix  C. 

The  United  States  having  ratified  the  London  Convention,  the  operating 
rules  provided  by  that  convention  are  incorporated  in  the  extracts  from 
"  Commercial  Traffic  Eegulations,"  U.  S.  Kaval  Communication  Service, 
printed  in  Appendix  B. 

The  conventional  abbreviation  signals,  authorized  by  the  London  Con- 
vention, and  which  are  used  by  naval  shore  stations  when  practicable,  will 
be  found  in  this  chapter,  after  the  code.     (Art.  255.) 

Information — relative  to  naval  shore  stations  open  to  commercial  busi- 
ness, lists  of  such  stations,  message  rates,  names  of  stations  and  hours  of 
sending  out  time  signals  for  the  use  of  navigators  in  comparing  chronom- 
eters, weather  reports  and  storm  warnings — is  issued  in  "  Notices  to 
Mariners "  and  shown  in  pilot  charts  published  by  the  U.  S.  Naval 
Hydrographic  Office. 

In  accordance  with  the  Berlin  Convention,  all  stations  have  three  call 
letters.  Groups  of  call  letters  are  assigned  to  nations  for  their  exclusive 
use  by  the  Bureau  of  the  International  Telegraph  Union  at  Berne,  Switzer- 
land.   (All  international  cable  accounts  are  settled  through  this  Bureau.) 

Specific  call  letters  from  these  groups  are  assigned  to  each  ship  and 
shore  stations  by  the  governments  of  the  respective  countries. 

To  the  United  States  has  been  assigned  all  combinations  of  letters 
beginning  with  N  and  W  and  the  combinations  KIA  to  KZZ. 

A  list  of  call  letters  will  be  found  in  "  Wireless  Telegraph  Stations  of  the 
World,"  published  by  the  Department  of  Commerce.  It  can  be  obtained 
from  the  Superintendent  of  Public  Documents  at  Washington.  This  will 
eventually  be  an  international  publication  issued  by  the  Berne  office, 

Eules  governing  the  licensing  of  commercial  and  private  stations  and 
operators  are  issued  by  the  Department  of  Commerce  and  inspections  to 
determine  their  compliance  with  the  laws  printed  in  Appendix  D  and  with 
the  London  Convention,  are  made  by  that  department. 

All  matters  pertaining  to  the  operation  of  U.  S.  Naval  Eadio  stations, 
both  high-powered  and  coastal  stations,  and  their  relations  with  com- 
mercial stations  afloat  and  ashore,  in  the  United  States  and  foreign 
countries,  are  under  the  supervision  of  the  Director  Naval  Communica- 
tions, Navy  Department,  Washington. 


APPENDICES. 


NOTE  1. 


The  following  list  of  metals  is  arranged  in  such  order  that  any  one  will 
be  the  positive  pole  of  the  battery  when  used  with  the  metal  next  below  it 
on  the  list  as  a  battery  element  and  the  negative  pole  when  used  with  the 
element  next  above  it,  the  difference  of  potential  between  any  two  being 
greater  the  farther  apart  they  are  in  the  series. 


Carbon, 

Silver. 

Lead. 

Zinc. 

Platinum. 

Copper. 

Cadmium. 

Magnesium, 

Gold. 

Iron. 

Tin. 

Sodium. 

The  amount  of  potential  difference  also  depends  on  the  battery  solution, 
and  in  some  instances  it  may  be  reversed.  Commercial  primary  batteries  are 
of  copper  and  zinc,  with  an  E.  M.  F.  of  approximately  1  volt,  and  carbon  and 
zinc,  with  an  E.  M.  F.  varying  from  1.4  in  LeclanchS  cells  and  some  dry  cells  to 
2.1  in  some  types  of  wet  cells,  depending  on  the  electrolyte. 

NOTE  2. 

The  relations  existing  between  electricity  and  matter  have  been  most  ex- 
haustively investigated  by  Prof.  J.  J.  Thomson,  who  has  proved  that  electric- 
ity has  an  atomic  structure  and  that  it  can  exist  separately  from  an  atom 
of  matter. 

When  a  current  is  sent  through  a  vacuum  tube,  the  luminous  beam  pro- 
ceeding from  the  cathode  has  been  shown  to  consist  of  particles  projected 
from  the  cathode.  These  particles  are  capable  of  turning  a  small  wheel. 
The  cathode  beam  can  be  deflected  by  either  a  magnetic  or  an  electric  field, 
and  it  is  found  to  consist  of  particles  of  negative  electricity  or  of  parts  of 
the  atom  negatively  charged,  each  having  about  one  eighteen-hundredth  of  the 
mass  of  an  atom  of  hydrogen. 

These  particles  are  the  same,  no  matter  what  gas  is  used  in  the  vacuum 
tube.  They  are  usually  called  electrons.  "When  an  electron  is  broken  off 
from  an  atom,  the  remaining  part  is  positively  charged.  Currents  of  elec- 
tricity, however  produced,  are  the  result  of  the  decomposition  of  atoms  into 
positive  and  negative  electric  charges.  There  can  be  no  electric  current 
without  movement  of  electrons.  Conductors  are  bodies  in  which  the  break- 
ing up  of  atoms  and  movements  of  electrons  take  place  more  or  less  easily. 
Some  free  electrons  exist  in  all  bodies.  It  is  by  setting  these  into  vibration 
and  by  means  of  this  vibration  making  them  break  off  similar  particles  from 
neighboring  atoms,  and  thus  propagate  the  disturbance  throughout  the  mass 
of  the  conductor,  that  electric  currents  are  generated. 

15 


326 


APPENDICES. 


APPENDIX  A. 


TABLE  1. 


[Extract  from  Fleming's  Cantor  lecture.  Journal  of  Society  of  Arts,  p,  1S6, 
January  5,  1906.  Taken  mostly  from  A.  Heydweiller,  "  On  Spark  Poten- 
tials."   Ann.  der  Physik,  vol.  248,  p.  235  (1898).] 


Spark  Voltage  Between  Brass  Balls  2  Centimeters  in  Diameter  for 
Various  Spark  Lengths. 


Spark  length  (cms.). 


Spark 
voltag«3. 

0.1 4,700 

0.2 8,100 

0.3 11,400 

0.4 14,500 

0.5 17,500 

0.6 20,400 

0.7 23,250 

0.8 26,100 

0.9 28,800 


Spark  length  (cms.). 


Spark 
voltage. 

1    31,300 

1.5 40,300 

2    47,400 

2.5 53,000 

3    57,500 

3.5 61,100 

4    64,200 

4.5 67,200 

5    69,800 


TABLE  lA. 


Material. 


Specific 
inductive 
capacity. 


Air    1 

Hard  rubber 2.29 

India  rubber 2.10 

Mica    6.64 

Micanite 

Typewriter  linen  paper  

Paraffin  oil   2.71 

Glass  (crown)    6.96 

Glass  (plate)    8.45 

Glass   (ligbt  flint)    6.72 

Glass  (extra  dense  flint)   9.86 

Porcelain  4.38 

Shellac  3.10 

•  Per  millimeter  for  thicknesses  up  to  1  millimeter. 
2  Per  centimeter. 


Dielectric 
strength. 

Volts. 

(  M,500 

(  «  3,000 

•  40,000 
» 30,000 
» 60.000 

•  40,000 

•  45,000 
•  7,000 


20,000 


r  9, 

tl6. 


9,000 
000 


3  Per  millimeter 
*  Approximate. 


APPENDICES.  227 

TABLE  2. 

Condenser  Capacity  Required  to  Give  Full        <sr.o,-ir  'L-r.^taa-a 
Power  for  Spark  Voltage  of  30.000  (0.4"  Gap)  '^  «^f^ii  TiJir 

K.W.  and  One  Discharge  Per  Half  Cycle.  (0  15"pap). 

60  cycles.  120  cycles  460  cycles  ^^  cycles. 

1   0.019  m.  f.  0.009  m.  f.  0.002  m.  f.  0.010  m.  f. 

2J 0.047     "  0  023     '•  0.006     "  0.025     " 

5   0.093     "  0.047     "  0.012     "  0.050     " 

10 0.185     "  0.093     "  0.024     "  0.100     " 

15 0.278     "  0.139     "  0.036     "  0.150     ' 

35  0.648     "  0.324     "  0.085     "  0,350     " 

1  standard  jar  condenser  =  0.002  m.  f. 

_  microfarads  X  spark  voltage  X  spark  voltage  X  spark  frequency 
^"  ^'  ~  2;oo^,ooo,ood 

TABLE  3. 

Incbease  of  Resistance  of  Coppeb  Wibe  ai  a  Frequency  of  400,000  Pkb 
Second  (750  Meteb  Wave  Length). 

Diameter  Increase 

of  wire.  in  resistance. 

0.2  mm.  1  per  cent. 

0.4     "  22 

0.8    "            .  120 

2.0    "  650 

4.0     "  1000 

TABLE  4. 

Specific  Resistance  of  Water  and  Soils. 

Sea  water    100 

Fresh  water   100,000 

Damp  soil   10,000  —  100,000 

Dry  soil   >1,000,000 

TABLE  5. 

LoGABiTHiiic  Decrement  (5)  of  Wave  Train  and  the  Approximate  Number 

OF  Waves  (N.)  in  the  Train  Before  the  Amplitude  Falls 

to    One-Tenth   of   the   Maximum. 


i 

N 

1.0 

3.5 

0.8 

4.0 

.6 

6.0 

.4 

7.0 

.3 

8.5 

.8 

12.5 

8 

V 

.1 

24.0 

.08 

30.0 

.06 

39.0 

.04 

58.0 

.03 

78.0 

.02 

116.0 

Good  tuning  is  not  possible  with  less  than  fifteen  waves  in  the  train. 


228  APPENDICES. 

TABLE  6. 

Some  Common  Units  Expressed  in  Terms  of  Absolute  Units, 

1  microfarad  =  1  .  10-ib  c.  g.  s. 

1  millihenry  =  1  .  108 

1  microhenry  =  1  .  lOs 

1  volt  =  1  .  108 

1  ohm  =  1  .  10» 

1  ampere  =  1  .  lO-i 

1  watt  =  1  .  107 


TABLE  7. 

Some  Common  Hiqh-Frequenct  Equations. 
The  time  of  oscillation  of  a  condenser  circuit  is 
r=  27r  »y LC  seconds. 
(1/  in  henries,  0  in  farads.) 

V  =  n'/.  and  T  =  —  , 

where  v  is  the  velocity,  n  the  frequency,  and  X  the  wave  length. 
The  wave  length  Is  therefore 

A  =  1.885  s/Za  .109  meters. 
In  a  condenser  charged  ?^  times  per  second  the  energy  passing  through  In 
one  second  is 

P  =  I  -y^  N  watts. 

(G  in  microfarads  and  F  in  volts.) 
The  damping  of  a  single  circuit  is 

(R  In  ohms  and  L  in  henries  or  both  in  absolute  units.) 
The  damping  of  two  circuits  by  the  resonance  method. 


'^^'^--^  -^;;ry  w-r^' 


The  following  equation  and  tables  are  the  results  of  experiments  conducted 
between  Brant  Rock  station  and  the  cruisers  Salem  and  Birmingham  In 
1909-10.  See  "  Some  Quantitative  Experiments  in  Long  Distance  Radio* 
Telegraphy,"  by  L.  W.  Austin,  Reprint  No.  159,  from  Bulletin  Bu.  of  Stand- 
ards, Vol.  7,  No.  3,  Feb.  1,  1911. 


APPENDICES. 


229 


Equation 


/„  =  4.25  X  /o  X 


hi  Ag 


ad 


I  =  Antenna  current,  sending,  in  amperes. 
Zg  =  Antenna  current,  receiving,  amperes  through  25  ohms. 
h,  =  Height  of  flat-top  antenna,  sending  station.  In  kilometers. 
h,  —  Height  of  flat-top  antenna,  receiving  station,  In  kilometers. 

n  =  .0015. 

d  =  Distance  in  kilometers, 

/  =  Wave  length  In  kilometers, 

e  =  2,7183. 

25  ohms  =  high-frequency  resistance  of  ship  aerial  of  1000-meter  wave 
length. 

The  above  equation  covers  the  normal-day  received  current  over  salt  water, 
through  25  ohms  for  two  stations  with  flat-top  aerials  of  any  height,  with  any 
value  of  sending  current  and  any  wave  length,  provided  the  sending  station 
is  so  coupled  as  to  give  but  one  wave  length. 

The  following  tables  (8,  9,  10  and  11,  12)  illustrate  the  application  of  this 
equation : 

TABLE  8. 

For  good  communication  received  current  should  be  equal  to  i«=40  X  10-« 
amperes  through  25  ohms  =  40  X  lO-*"  watts  =  *  erg  per  second. 

For  audible  signals  7^=10  X  lO-s  amperes  through  25  ohms  =  2,5  X  10-» 
watts  =jV6rg  per  second. 

TABLE  9. 


Calculated  Relation  between  Antenna  Current  and  Distance  for  Two  Ships  with 

Antenna  Heights  of  130  Feet, 

A  =  1000  m. 


Antenna  Current 

Working  Distance 
40.10-*  amp. 

Extreme  Distance  of  Audibility 
10.10-«amp, 

Is. 

Day. 

Night, 
(Zero  Absorption) 

Day. 

Night. 
(Zero  Absorption) 

1  amp. 

76  miles 

90  miles 

200  miles 

360  miles 

3 

135 

180 

300 

720 

3 

180 

270 

375 

1080 

6 

235 

460 

475 

1800 

7 

280 

630 

550 

2520 

.         10 

346 

900 

6.30 

3600 

16 

420 

1360 

726 

6400 

20 

475 

1800 

790 

7200 

26 

535 

2260 

840 

9000 

30 

666 

2700 

900 

10800 

40 

630 

3600 

970 

14400 

60 

686 

4600 

1026 

18000 

60 

726 

6400 

1150 

21600 

230 


APPENDICES. 


TABLE  10. 


Good  Working  Distance  and  Sending  Current  for  Two  Stations  with  Flat-Top  Antennas 

450  Feet  High. 


Nautical  Miles. 

A  =  1000  m. 

A  =  3500  m. 

A  =  3760  m. 

A  =  6000  m. 

1000 

15  amp. 

13.5  amp. 

15  amp. 

17  amp. 

1250 

38 

27 

27 

30 

1500 

91 

49 

44 

46 

1760 

200 

95 

77 

74 

2000 

490 

155 

122 

105 

2260 

246 

200 

160 

2600 

470 

314 

236 

2750 

500 

336 

3000 

... 

775 

600 

APPENDICES. 


231 


CO    en 

S 

00 

t- 

<o 

10     CI 

•"< 

^*    i— 1 

B 

?^ 

» 

Q 

0 

,^ 

^^ 

0   ua 

OS 

10    CO 

IT) 

0 

0    0 

s 

^ 

<o 

t- 

g 

^ 

g 

CO 

11 

II 

IS 

N    0 

-< 

;4 

^1- 

§ 

0 

s 

g 

§ 

>o 

^   g 

?,' 

00     lO 

IM 

OS 

«-    <o 

^  s 

• 

■* 

CO 

N    •* 

■a 

00 

a 

6 

a 

s 

eo 

Tl 

,^ 

«o    -* 

lil 

0 

0  0 

0 

p 

^ 

'^ 

CO 

■o 

CO 

ai 

■* 

10  rt 

II 

II 

. 

^ 

^ 

<o 

N 

t-    00 

g 

SP  :?: 

OS 

■* 

rt     OS 

•< 

W 

Wp 

3; 

{0 

Of 

■* 

a> 

'"' 

" 

" 

" 

«c 

03     CO 

^_^ 

S  ?§ 

s 

«o 

CO    CO 

e»   0 

a 

« 

^ 

,_, 

f^-* 

tn 

CO 

CO 

tl 

0 

0  0 

00 

l-H 

0 

05 

pa 

10 

CO   ffi 

'"' 

^ 

»< 

(M 

II 

II 

•* 

^-t 

00 

CO 

CO    ■# 

-< 

^i^ 

s 

js 

CO 

CO 

5 

00 

0 

s  ?i 

-** 

U3 

5  §§ 

s 

C-l 

t-   ■* 

(M 

to 

(Y) 

la 

00     -H 

g  B 

CO     -H 

00 

>C     OS 

fl 

Si 

Oh 

<-> 

m 

c? 

t-     CO 

,—4 

0 

0   0 

II 

^ 

CO 

00 

Wta 

i 

kn 

,— , 

0 

•«  0 

g 

e<  0 

00 

«n 

;*  ■* 

-< 

bj 

2? 

?i 

f« 

;?; 

■*  ©1 

t-    so 

CO 

'^ 

OS 

■* 

C5 

0 

CO    0 

ffi 

a 

« 

s 

3 

(— , 

j^ 

<-) 

V 

03 

e^   ->j< 

to    CO 

,^ 

0   0 

^ 

2 

00 

CO 

ou 

S 

II 

©I 

II 

w 

s 

0 

0 

10 

,« 

5  ?s 

< 

W|-o 

s 

-<J* 

s 

CO 

0    OS 

lO 

«o   0 

& 

N   00 

00 

OS     0 

10 

S 

^  ^ 

a 

oi 

^^ 

(^ 

r-> 

rrt 

10 

t- 

0   -* 

(M 

<-) 

0 

0   0 

S8 

?g 

^ 

-* 

w 

cs 

CO 

II 

-< 

II 

Wl-a 

g 

§ 

g 

i 

8  g 

11 

10 

5f? 

s  g 

0 
IM 

g 

?2  g 

OS 

CO 

g 

a 

ci. 

a: 

g 

8 

S 

g 

«? 

to 

10   III 

t- 

C'l    0 

0 

0 

II 

tr 

10 

«o 

•^ 

11 

W'ts 

g 

i 

S  8  8 

s  2  y 

05 

f?  8  g 

t-    <o    -* 

MM 

0 

2 

5  1 

10 

Tl£ 

CO 

Cl 

10 

0 

ID 

0 

P,  2 

S   S    e-i 

s 

8 

i§ 

u 

rt   CJ 

I! 

-«>   10 

« 

•5  a 

?i 

s 

0 

8  g  g 

8  8  8 

8  8 

g 

g 

g  B 

s? 

'"'   '"' 

'^ 

M 

ei   CO 

Z 

"X  « 


g 

00  '«  o>  ee     • 

<o    00   OS    r-^   IS    eo   1-1      * 
3   i-   CO   CO   o«   «   <-c     • 

to 

si  ig  g  8  8  8  1    : 

2 
II 

cS 

■*   us         t-      . 

1  g  §  S  2  2  *    : 

^ 

32.5  ft. 

66 
100 
ICO 
200 
3(10 
460 

II 

i-i  B 

c« 

78 
39 
26.3 
19.5 
15.8 
8.5 
5.66 

J3 

32.5  ft. 

66 
100 
130 
160 
300 
460 

g 

T 

.4 

cs 

us     CO    CO     t-     ^     «D    t2        : 
J*    t^    ~    06    I-    10    CO       • 

32.6  ft. 

66 
100 
130 
160 
200 
300 

09 

CO 

00   fr-    »   10 

1 

II 

""          1 

32.6  ft. 

66 
100 
130 
160 
200 
300 
460 

232  APPENDICES. 

APPENDIX  B. 

Extracts  from  Commeecial  Traffic  Regulations,  U.  S.  Naval 

Communication  Servick 

(These  rules  are  changed  as  circumstances  require.) 

"  Two  wave  lengths,  one  of  600  meters  and  the  other  of  300  meters,  are 
authorized  for  general  public  service.  All  naval  stations,  ships  and  coastal, 
must  use  these  wave  lengths  when  communicating  with  commercial  ships.  In 
general,  commercial  work  shall  be  entirely  on  commercial  tunes. 

All  naval  stations  (ship  and  shore)  shall  listen  on  600  meters  for  at  least 
three  minutes  during  each  quarter  of  the  hour,  local  standard  time,  the  listen- 
ing period  to  commence  at  10,  25,  40  and  55  minutes  after  each  hour,  thereby 
assigning  a  regular  period  for  listening  on  600  meters.  Should  a  naval  station 
receive  a  call  from  a  ship  during  such  listening  period  at  a  time  when  com- 
munication with  another  ship  or  station  has  not  been  completed,  such  station 
should  request  (by  conventional  signal)  the  calling  ship  to  wait,  and  when 
the  listening  period  has  elapsed  clear  the  station  which  was  first  in  commu- 
nication. After  such  station  has  been  cleared,  the  station  should  then  clear 
the  calling  ship. 

Stations  having  the  distant  control  in  operation  working  similar  stations 
shall  observe  the  listening  in  requirements  on  the  short  wave  antenna  only, 
as  it  is  not  intended  to  disturb  communication  on  the  long  wave  lengths  at  such 
stations. 

Stations  having  distant  control  transmitting  to  stations  not  employing  dis- 
tant control  should  cease  sending  during  the  listening  in  period  in  order  to 
permit  the  receiving  station  to  observe  this  regulation. 

A  wave  length  of  1800  meters  is  authorized  for  certain  communication. 

Position  Reports. 
As  soon  as  the  coastal  station  has  answered,  the  shipboard  station  shall 
furnish  it  with  the  following  data  in  case  it  has  messages  to  transmit;  such 
data  shall  likewise  be  furnished  upon  request  from  the  coast  station.     This 
report  shall  be  preceded  by  the  letters  TR: 

(a)  The  approximate  distance,  in  nautical  miles,  of  the  vessel  from  the 
coast  station. 

(b)  The  position  of  the  vessel  indicated  in  a  concise  form  and  adapted  to 
the  circumstances  of  the  case. 

(c)  Her  next  port  of  call. 

id)  The  number  of  radiograms,  if  the  total  number  of  words  therein  does 
not  exceed  50,  otherwise  the  number  of  words. 

Items  (a),  (6),  and  (c)  shall  be  obtained  from  authorized  official  sources. 

The  speed  of  the  ship  in  nautical  miles  shall  also  be  given  if  specially  re- 
quested by  the  coast  station. 

Example. 

TR 

50 

Off  Cape  Canaveral 

Vera  Cruz 

3 


KSA 
The  various  items  may  be  designated  by  the  signals  QRB,  etc. 


APPENDICES.  233 

NuMBEB  OF  Message. 

Each  message,  regardless  of  class,  sent  by  a  ship  or  station,  will  be  num- 
bered in  sequence,  the  first  message  of  each  day  sent  to  a  certain  ship,  station, 
or  land  line  office,  to  be  numbered  "  1."  This  number  is  known  as  the  "  station  " 
number.  Each  ship  or  station  will  have  a  separate  series  of  numbers  for  each 
station  or  land  line  office  to  which  it  transmits,  a  new  series  beginning  each 
day  at  midnight. 

The  receiving  number  is  that  given  by  the  ship,  station,  or  office  received 
from,  and  will  not  be  transmitted;  but  a  new  number  will  be  assigned,  in 
case  the  message  is  retransmitted,  which  will  be  the  next  number  in  sequence 
for  the  station  sent  to.  The  number  will  be  transmitted  immediately  after 
the  name  of  office  of  origin  without  the  abbreviation  "  No."  or  "  Nr."  In 
receiving  a  series  of  messages  the  sequence  of  the  numbers  will  be  noted, 
and  in  case  a  break  in  the  sequence  should  occur,  inquiry  for  the  missing 
message  shall  be  made  immediately. 

Examples. 

(1)  The  first  10  commercial  messages  received  at  a  station  on  a  certain 
day  are  from  the  S.  S.  Amazon.  They  should  be  numbered  1-10  by  the  Amazon. 
The  next  two  commercial  messages  are  from  the  Reid,  numbered  1  and  2  by 
the  Reid. 

(2)  The  next  two  messages  from  the  Reid  are  sent  to  S.  S.  Baltimore  direct. 
They  should  also  be  numbered  1  and  2  by  the  Reid. 

(3)  All  of  the  messages  received  by  the  station  from  the  Amazon  and  the 
Reid  are  turned  over  to  a  land  line  or  cable  office  for  further  transmission 
with  the  numbers  1-12,  being  the  first  messages  sent  that  date  through  that 
office. 

Counting  of  Words. 

GENERAL. 

The  word  (cable)  system  of  counting  shall  be  observed,  and  all  words  in 
the  address,  text,  and  signature  must  be  counted  and  charged  for. 

No  item  in  the  preamble  will  be  counted,  but  the  abbreviated  supplementary 
instructions,  transmitted  as  the  first  item  of  the  address  in  the  case  of  radio- 
grams of  special  classes,  shall  be  counted  and  charged  as  one  word.  If  a 
route  is  designated  in  the  address,  it  shall  be  counted  and  charged  for. 

Text. 

plain  language. 

In  a  message  written  entirely  in  plain  language,  the  maximum  length  of 

chargeable  words  is  fixed  at  15  characters.    "Words  of  more  than  15  characters 

are  charged  at  the  rate  of  one  word  for  every  15  characters  or  fraction  thereof. 

CODE  LANGUAGE, 

In  code  messages,  the  maximum  length  of  the  chargeable  (pronounceable) 
word  is  fixed  at  10  characters. 

Code  words  of  more  than  10  letters  must  be  counted  and  charged  at  the 
cipher  rate — that  is,  five  letters  to  a  word — and  noted  in  the  check;  but  genuine 
words  of  more  than  10  letters  may  be  used  in  their  original  sense,  and  may  be 
counted  at  the  rate  of  10  letters  to  the  word.  Code  may  be  made  up  of  dic- 
tionary or  artificial  words,  but  artificial  words  must  be  pronounceable  to  obtain 


234  APPENDICES. 

the  10-letter  count — artificial  words  not  pronounceable  are  counted  at  the 
rate  of  five  letters  to  a  word. 

Combinations  or  alterations  of  words  concealed  by  reversing  the  order  of 
the  letters  or  syllables  will  not  be  accepted  as  code  words. 

CIPHEB  LANGUAGE. 

In  cipher,  the  letters  or  figures  in  each  uninterrupted  series  shall  be  counted 
at  the  rate  of  five,  or  a  fraction  of  five,  as  one  word.  Groups  of  letters  are 
charged  at  the  same  rate  as  groups  of  figures,  but  figures  and  letters  must  be 
counted  separately;  thus  A5C  counts  as  three  words. 

MIXED  LANGUAGE. 

In  messages  written  in  code  and  plain  language,  the  maximum  length  of 
word  chargeable  is  10  characters. 

In  messages  containing  plain  language  and  cipher  the  words  in  passages 
in  plain  language  are  charged  at  the  rate  of  one  word  for  every  15  characters 
or  fraction  thereof,  and  the  groups  in  the  passages  in  cipher  language  at  the 
rate  of  one  word  for  every  five  characters  or  fraction  thereof. 

In  messages  written  in  plain  language,  code  language,  and  cipher  language, 
the  words  in  the  passages  in  plain  language  and  code  language  are  charged 
as  code  language,  and  the  passages  in  cipher  language  are  charged  as  cipher 
language. 

SRS    NUMBEE. 

For  the  purpose  of  accounting,  each  commercial  (including  paid  service) 
message  is  given  a  number  known  as  the  SRS  number,  but  this  number  is 
never  transmitted  by  radio  nor  over  telegraph  lines  or  cables.  Relayed  com- 
mercial messages  are  given  an  SRS  number  followed  by  capital  letter  R.  All 
service  messages  sent  concerning  a  commercial  message  are  given  the  SRS 
number  of  the  message  to  which  they  refer,  followed  by  small  letter  "  a  " 
for  the  first  service,  "  b  "  for  the  second,  and  so  on.  In  the  event  a  message 
is  cancelled  after  an  SRS  number  has  been  assigned  to  it,  the  number  assigned 
shall  remain  and  the  message  forwarded  with  the  traffic  to  the  director  with 
an  explanation  on  message  copy  as  to  the  reason  for  cancellation. 


APPENDICES.  235 

APPENDIX  C.   • 

Extracts  from  Convention,  Final  Protocol,  and  Service  Regulations. 

(Agreed  upon  at  London,  July  15,  1912.    Ratified  by  U.  S.  Senate,  Jan.  22,  1913. 

Put  into  operation,  July  1,  1913.) 

CONVENTION. 

Article  2. 

By  "  coastal  stations  "  is  to  be  understood  every  radio  station  established 
on  shore  or  on  board  a  permanently  moored  vessel  used  for  the  exchange  of 
correspondence  with  ships  at  sea. 

Every  radio  station  established  on  board  any  vessel  not  permanently  moored 
is  called  a  "  station  on  shipboard." 

Article  3. 

The  coastal  stations  and  the  stations  on  shipboard  shall  be  bound  to  exchange 
radiograms  without  distinction  of  the  radio  system  adopted  by  such  stations. 

Every  station  on  shipboard  shall  be  bound  to  exchange  radiograms  with 
every  other  station  on  shipboard  without  distinction  of  the  radio  system 
adopted  by  such  stations. 

However,  in  order  not  to  impede  scientific  progress,  the  provisions  of  the 
present  Article  shall  not  prevent  the  eventual  employment  of  a  radio  system 
incapable  of  communicating  with  other  systems,  provided  that  such  incapacity 
shall  be  due  to  the  specific  nature  of  such  system  and  that  it  shall  not  be  the 
result  of  devices  adopted  for  the  sole  purpose  of  preventing  intercommuni- 
cation. 

Article  4. 

Notwithstanding  the  provisions  of  Article  3,  a  station  may  be  reserved  for 
a  limited  public  service  determined  by  the  object  of  the  correspondence  or 
by  other  circumstances  independent  of  the  system  employed. 

Each  of  the  High  Contracting  Parties  reserves  the  right  to  prescribe  or 
permit  at  the  stations  referred  to  in  Article  1,*  apart  from  the  installation  the 
data  which  are  to  be  published  in  conformity  with  Article  6,t  the  Installation 
and  working  of  other  devices  for  the  purpose  of  establishing  special  radio 
communication  without  publishing  the  details  of  such  devices. 

Article  8. 
The  working  of  the  radio  stations  shall  be  organized  as  far  as  possible  in 
such  manner  as  not  to  disturb  the  service  of  other  radio  stations. 

Article  9. 
Radio  stations  are  bound  to  give  absolute  priority  to  calls  of  distress  from 
whatever  source,  to  similarly  answer  such  calls  and  to  take  such  action  with 
regard  thereto  as  may  be  required. 

*  Open  to  public  service. 

t  Names  of  stations  and  data  necessary  to  facilitate  exchange  of  radiograms. 


236  APPENDICES. 

Article  10. 
The  charge  for  a  radiogram  shall  comprise,  according  to  the  circumstances: 

1.  (a)   The  coastal  rate,  which  shall  fall  to  the  coastal  station; 
(b)   The  shipboard  rate,  which  shall  fall  to  the  shipboard  station. 

2.  The  charge  for  transmission  over  the  telegraph  lines,  to  be  computed 
according  to  the  ordinary  rules. 

3.  The  charges  for  transit  through  the  intermediate  coastal  or  shipboard 
stations  and  the  charges  for  special  services  requested  by  the  sender. 

The  coastal  rate  shall  be  subject  to  the  approval  of  the  Government  of  which 
the  coastal  station  is  dependent,  and  the  shipboard  rate  to  the  approval  of  the 
Government  of  which  the  ship  is  dependent. 

Article  13. 

The  International  Bureau  of  the  Telegraph  Union  shall  be  charged  with 
collecting,  coordinating  and  publishing  information  of  every  kind  relating  to 
radiotelegraphy,  examining  the  applications  for  changes  in  the  Convention  or 
Regulations,  promulgating  the  amendments  adopted,  and  generally  performing 
all  administrative  work  referred  to  it  in  the  interest  of  international  radio- 
telegraphy. 

The  expense  of  such  institution  shall  be  borne  by  all  the  contracting 
countries. 

Article  14. 

Each  of  the  High  Contracting  Parties  reserves  to  itself  the  right  of  fixing 
the  terms  on  which  it  will  receive  radiograms  proceeding  from  or  intended 
for  any  station,  whether  on  shipboard  or  coastal,  which  is  not  subject  to  the 
provisions  of  the  present  Convention. 

If  a  radiogram  is  received  the  ordinary  rates  shall  be  applicable  to  it. 

Any  radiogram  proceeding  from  a  station  on  shipboard  and  received  by  a 
coastal  station  of  a  contracting  country,  or  accepted  in  transit  by  the  adminis- 
tration of  a  contracting  country,  shall  be  forwarded. 

Any  radiogram  intended  for  a  vessel  shall  also  be  forwarded  if  the  adminis- 
tration of  the  contracting  country  has  accepted  it  originally  or  in  transit  from 
a  non-contracting  country,  the  coastal  station  reserving  the  right  to  refuse 
transmission  to  a  station  on  shipboard  subject  to  a  non-contracting  country. 

Article  21. 

The  High  Contracting  Parties  shall  preserve  their  entire  liberty  as  regards 
radio  installations  other  than  provided  for  in  Article  1,  especially  naval  and 
military  installations,  and  stations  used  for  communications  between  fixed 
points.  All  such  installations  and  stations  shall  be  subject  only  to  the  obliga- 
tions provided  for  in  Articles  8  and  9  of  the  present  Convention. 

However,  when  such  installations  and  stations  are  used  for  public  maritime 
service  they  shall  conform,  in  the  execution  of  such  service,  to  the  provisions 
of  the  Regulations  as  regards  the  mode  of  transmission  and  rates. 

On  the  other  hand,  if  coastal  stations  are  used  for  general  public  service 
with  ships  at  sea  and  also  for  communication  between  fixed  points,  such  stations 
shall  not  be  subject,  in  the  execution  of  the  last  named  service,  to  the  pro- 
visions of  the  Convention  except  for  the  observance  of  Articles  8  and  9  of  this 
Convention. 


APPENDICES.  237 

Nevertheless,  fixed  stations  used  for  correspondence  between  land  and  land 
shall  not  refuse  the  exchange  of  radiograms  with  another  fixed  station  on  ac- 
count of  the  system  adopted  by  such  station;  the  liberty  of  each  country  shall, 
however,  be  complete  as  regards  the  organization  of  the  service  for  corre- 
spondence between  fixed  points  and  the  nature  of  the  correspondence  to  be 
effected  by  the  stations  reserved  for  such  service. 

Akticle  22. 

The  present  Convention  shall  go  into  effect  on  the  1st  day  of  July,  1913, 
and  shall  remain  in  force  for  an  indefinite  period  or  until  the  expiration  of 
one  year  from  the  day  when  it  shall  be  denounced  by  any  of  the  contracting 
parties. 

Such  denunciation  shall  affect  only  the  Government  in  whose  name  it  shall 
have  been  made.  As  regards  the  other  Contracting  Powers,  the  Convention 
shall  remain  in  force. 

Extracts  from  Final  Protocol. 

II. 

Note  is  taken  of  the  following  declaration: 

The  Delegation  of  the  United  States  declares  that  its  government  is  under 
the  necessity  of  abstaining  from  all  action  with  regard  to  rates,  because 
the  transmission  of  radiograms  as  well  as  of  ordinary  telegrams  in  the  United 
States  is  carried  on,  wholly  or  in  part,  by  commercial  or  private  companies. 

III. 

Note  is  likewise  taken  of  the  following  declaration : 

The  Government  of  Canada  reserves  the  right  to  fix  separately,  for  each  of 
its  coastal  stations,  a  total  maritime  rate  for  radiograms  proceeding  from 
North  America  and  destined  for  any  ship  whatever,  the  coastal  rate  amounting 
to  three-fifths  and  the  shipboard  rate  to  two-fifths  of  the  total  rate. 

Extracts  from  Service  Regitlations  Affixed  to  the  International  Radio- 
telegraph Convention,  London,  1912. 

1.  organization  of  radio  stations. 

Article  I. 

The  choice  of  radio  apparatus  and  devices  to  be  used  by  the  coastal  stations 
and  stations  on  shipboard  shall  be  unrestricted.  The  installation  of  such 
stations  shall  as  far  as  possible  keep  pace  with  scientific  and  technical  progress. 

Article  II. 
Two  wave  lengths,  one  of  600  meters  and  the  other  300  meters,  are  authorized 
for  general  public  service.  Every  coastal  station  opened  to  such  service  shall 
be  equipped  in  such  manner  as  to  be  able  to  use  these  two  wave  lengths,  one  of 
which  shall  be  designated  as  the  normal  wave  length  of  the  station.  During  the 
whole  time  that  a  coastal  station  is  open  it  shall  be  in  condition  to  receive  calls 
according  to  its  normal  wave  length.  For  the  correspondence  specified  under 
paragraph  2  of  Article  XXXV,  however,  a  wave  length  of  1,800  meters  shall 


238  APPENDICES. 

be  used.  In  addition,  each  Government  may  authorize  in  coastal  stations  the 
employment  of  other  wave  lengths  designed  to  insure  long-range  service  or 
any  service  other  than  for  general  public  correspondence  established  in  con- 
formity with  the  provisions  of  the  Convention  under  the  reservation  that  such 
wave  lengths  do  not  exceed  600  meters  or  that  they  do  exceed  1,600  meters. 

In  particular,  stations  used  exclusively  for  sending  signals  designed  to  deter 
mine  the  position  of  ships  shall  not  employ  wave  lengths  exceeding  150  meters 

Article  III. 

1.  Every  station  on  shipboard  shall  be  equipped  in  such  manner  as  to  be 
able  to  use  wave  lengths  of  600  meters  and  of  300  meters.  The  first  shall  be 
the  normal  wave  length  and  may  not  be  exceeded  for  transmission  except  in 
the  case  referred  to  under  Article  XXXV  (paragraph  2).* 

Other  wave  lengths,  less  than  600  meters,  may  be  used  in  special  cases  and 
under  the  approval  of  the  managements  to  which  the  coastal  and  shipboard 
stations  concerned  are  subject. 

2.  During  the  whole  time  that  a  station  on  shipboard  is  open  it  shall  be  able 
to  receive  calls  according  to  its  normal  wave  length. 

3.  Vessels  of  small  tonnage  which  are  unable  to  use  a  wave  length  of  600 
meters  for  transmission,  may  be  authorized  to  employ  exclusively  the  wave 
length  of  300;  they  must  be  able  to  receive  a  wave  length  of  600  meters. 

Article  IV. 
Communication  between  a  coastal  station  and  a  station  on  shipboard  shall 
be  exchanged  on  the  part  of  both  by  means  of  the  same  wave  length.  If, 
in  a  particular  case,  communication  is  difficult,  the  two  stations  may,  by 
mutual  consent,  pass  from  the  wave  length  with  which  they  are  communicat- 
ing to  the  other  regulation  wave  length.  Both  stations  shall  resume  their 
normal  wave  length  when  the  exchange  of  radiograms  is  finished. 

Aeticle  V. 

1.  The  International  Bureau  shall  draw  up,  publish,  and  revise  from  time 
to  time  an  official  chart  showing  the  coastal  stations,  their  normal  ranges, 
the  principal  lines  of  navigation,  and  the  time  normally  taken  by  ships  for 
the  voyage  between  the  different  ports  of  call. 

2.  It  shall  draw  up  and  publish  a  list  of  radio  stations  of  the  class  referred 
to  in  article  1  of  the  Convention,  and  from  time  to  time  supplements  covering 
additions  and  modifications.  Such  list  shall  contain  for  each  station  the  fol- 
lowing data: 

(1)  In  the  case  of  coastal  stations;  name,  nationality  and  geographical 
location  indicated  by  the  territorial  subdivision  and  the  latitude  and  longitude 
of  the  place;  in  the  case  of  stations  on  shipboard;  name  and  nationality  of  the 
ship;  when  the  case  arises,  the  name  and  address  of  the  party  working  the 
station ; 

(2)  The  call  letters  (the  calls  shall  be  distinguishable  from  one  another  and 
each  must  be  formed  of  a  group  of  three  letters) ; 

(3)  The  normal  range; 

(4)  The  radio  system  with  the  characteristics  of  the  transmitting  system 
(musical  sparks,  tonality  expressed  by  the  number  of  double  vibrations,  etc.) ; 

(5)  The  wave  lengths  used  (the  normal  wave  length  to  be  underscored) ; 

(6)  The  nature  of  the  services  carried  on; 

*  Authorized  wave  length  of  1800  meters  for  special  purpose. 


APPENDICES.  239 

(7)  The  hours  during  which  the  station  is  open; 

(8)  When  the  case  arises,  the  hour  and  method  of  transmitting  time  signals 
and  meteorological  telegrams; 

(9)  The  coastal  rate  or  shipboard  rate. 

3.  The  list  shall  also  contain  such  data  relating  to  radio  stations  other  than 
those  specified  in  Article  I  of  the  Convention  as  may  be  communicated  to  the 
International  Bureau  by  the  management  of  the  Radio  Service  ("administra- 
tion ")  to  which  such  stations  are  subject,  provided  that  such  managements 
are  either  adherents  to  the  Convention  or,  if  not  adherents,  have  made  the 
declaration  referred  to  in  Article  XLVIII.* 

4.  The  following  notations  shall  be  adopted  in  documents  for  use  by  the 
International  Service  to  designate  radio  stations: 

PG  Station  open  to  general  public  correspondence. 
PR  Station  open  to  limited  public  correspondence. 
P  Station  of  private  interest. 

O  Station  open  exclusively  to  official  correspondence. 
N  Station  having  continuous  service. 
X  Station  having  no  fixed  working  hours. 

5.  The  name  of  a  station  on  shipboard  appearing  in  the  first  column  of  the 
list  shall  be  followed  in  case  there  are  two  or  more  vessels  of  the  same  name, 
by  the  call  letters  of  such  station. 

Article  VI. 

The  exchange  of  superfluous  signals  and  words  is  prohibited  to  stations 
of  the  class  referred  to  in  Article  I  of  the  Convention.  Experiments  and  prac- 
tice will  be  permitted  in  such  stations  in  so  far  as  they  do  not  interfere  with 
the  service  of  other  stations. 

Practice  shall  be  carried  on  with  wave  lengths  different  from  those  authorized 
for  public  correspondence,  and  with  the  minimum  of  power  necessary. 

Abticle  VII. 

1.  All  stations  are  bound  to  carry  on  the  service  with  the  minimum  of 
energy  necessary  to  insure  safe  communication. 

2.  Every  coastal  or  shipboard  station  shall  comply  with  the  following  require- 
ments: 

(a)  The  waves  sent  out  shall  be  as  pure  and  as  little  damped  as  possible; 
In  particular,  the  use  of  transmitting  devices  in  which  the  waves  sent  out 

are  obtained  by  means  of  sparks  directly  in  the  aerial  (plain  aerial)  shall  not 
be  authorized  except  in  cases  of  distress. 

It  may,  however,  be  permitted  in  the  case  of  certain  special  stations  (those 
of  small  vessels  for  example)  in  which  the  primary  power  does  not  exceed 
50  watts. 

(b)  The  apparatus  shall  be  able  to  transmit  and  receive  at  a  speed  equal 
to  at  least  20  words  a  minute,  words  to  be  counted  at  the  rate  of  5  letters  each. 

New  installations  using  more  than  50  watts  shall  be  equipped  in  such  a  way 
as  to  make  it  possible  to  obtain  with  ease  several  ranges  less  than  the  normal 
range,  the  shortest  being  approximately  15  nautical  miles.  Existing  installa- 
tions using  more  than  50  watts  shall  be  remodeled,  wherever  possible,  so  as 
to  comply  with  the  foregoing  provisions. 


*  Refers  to  routing  radiograms  through  countries  not  ratifying  London  Con- 
vention. 


240  APPENDICES. 

(c)  Receiving  apparatus  shall  be  able  to  receive,  with  the  greatest  possible 
protection  against  interference,  transmissions  of  the.  wave  lengths  specified 
in  the  present  Regulations,  up  to  600  meters. 

3.  Stations  serving  solely  for  determining  the  position  of  ships  (radiophares) 
shall  not  operate  over  a  radius  greater  than  30  nautical  miles. 

Abticle  VIII. 
Independently  of  the  general  requirements  specified  under  Article  VII,  sta- 
tions on  shipboard  shall  likewise  comply  with  the  following  requirements: 

(a)  The  power  transmitted  to  the  radio  apparatus,  measured  at  the  ter- 
minals of  the  generator  of  the  station,  shall  not,  under  normal  conditions,  ex- 
ceed one  kilowatt. 

(b)  Subject  to  the  provisions  of  Article  XXXV,  paragraph  2,*  power  exceed- 
ing one  kilowatt  may  be  employed  when  the  vessel  finds  it  necessary  to  corre- 
spond while  more  than  200  nautical  miles  distant  from  the  nearest  coastal 
station,  or  when,  owing  to  unusual  circumstances,  communication  can  be  estab- 
lished only  by  means  of  an  increase  of  power. 

Article  IX. 

1.  No  station  on  shipboard  shall  be  established  or  worked  by  private  enter- 
prise without  a  license  issued  by  the  Government  to  which  the  vessel  is 
subject. 

Stations  on  board  of  ships  having  their  port  of  registry  in  a  colony,  posses- 
sion, or  protectorate  may  be  described  as  subject  to  the  authority  of  such 
colony,  possession,  or  protectorate. 

2.  Every  shipboard  station  holding  a  license  issued  by  one  of  the  contracting 
Governments  shall  be  considered  by  the  other  Governments  as  having  an 
installation  fulfilling  the  requirements  stipulated  in  the  present  Regulations. 

Competent  authorities  of  the  countries  at  which  the  ship  calls  may  demand 
the  production  of  the  license.  In  default  of  such  production,  these  authorities 
may  satisfy  themselves  as  to  whether  the  radio  installations  of  the  ship  fulfill 
the  requirements  imposed  by  the  present  regulations. 

When  the  management  of  the  radio  service  of  a  country  is  convinced  by 
its  working  that  a  station  on  shipboard  does  not  fulfill  the  requirements,  it 
shall,  in  every  case,  address  a  complaint  to  the  management  of  the  radio 
service  of  the  country  to  which  such  ship  is  a  subject.  The  subsequent  pro- 
cedure, when  necessary,  shall  be  the  same  as  that  prescribed  in  Article  XII, 
paragraph  2. 

Article  X. 

1.  The  service  of  the  station  on  shipboard  shall  be  carried  on  by  a  telegraph 
operator  holding  a  certificate  issued  by  the  Government  to  which  the  vessel 
is  subject,  or,  in  case  of  necessity  and  for  one  voyage  only,  by  some  other 
adhering  Government. 

2.  There  shall  be  two  classes  of  certificates: 

The  first-class  certificate  shall  attest  the  professional  efiiciency  of  the  operator 
as  regards: 

(a)  Adjustment  of  the  apparatus  and  knowledge  of  its  functioning; 

(b)  Transmiss^pn  and  acoustic  reception  at  the  rate  of  not  less  than  20 
words  a  minute; 

(c)  Knowledge  of  the  regulations  governing  the  exchange  of  radio  corre- 
spondence. 

*  See  note,  bottom  page  239. 


APPENDICES.  241 

The  second-class  certificate  may  be  issued  to  operators  who  are  able  to  trans- 
mit and  receive  at  a  rate  of  only  12  to  19  words  a  minute  but  who,  in  other 
respects,  fulfill  the  requirements  mentioned  above.  Operators  holding  second- 
class  certificates  may  be  permitted  on: 

(a)  Vessels  which  use  radiotelegraphy  only  in  their  own  service  and  in  the 
correspondence  of  their  crews,  fishing  vessels  in  particular; 

(b)  All  vessels,  as  substitutes,  provided  such  vessels  have  on  board  at  least 
one  operator  holding  a  first-class  certificate.  However,  on  vessels  classed  under 
the  first  category  indicated  in  Article  XIII,  the  service  shall  be  carried  on  by 
at  least  two  telegraph  operators  holding  first-class  certificates. 

In  the  stations  on  shipboard,  transmissions  shall  be  made  only  by  operators 
holding  first  or  second-class  certificates  except  in  cases  of  necessity  where 
it  would  be  impossible  to  conform  to  this  provision. 

3.  The  certificate  shall  furthermore  state  that  the  Government  has  bound 
the  operator  to  secrecy  with  regard  to  the  correspondence. 

4.  The  radio  service  of  the  station  on  shipboard  shall  be  under  the  superior 
authority  of  the  commanding  officer  of  the  ship. 

Aeticlb  XI. 

Ships  provided  with  radio  installations  and  classed  under  the  first  two  cate- 
gories indicated  in  Article  XIII  are  bound  to  have  radio  installations  for 
distress  calls  all  the  elements  of  which  shall  be  kept  under  conditions  of  the 
greatest  possible  safety  to  be  determined  by  the  Government  issuing  the  license. 
Such  emergency  installations  shall  have  their  own  source  of  energy,  be  capable 
of  quickly  being  set  into  operation,  of  functioning  for  at  least  six  hours,  and 
have  a  minimum  range  of  80  nautical  miles  for  ships  of  the  first  category  and 
50  miles  for  those  of  the  second.  Such  emergency  installations  shall  not 
be  required  in  the  case  of  vessels  the  regular  installations  of  which  fulfill  the 
requirements  of  the  present  article. 

Aeticle  XII. 

If  the  management  of  the  radio  service  of  a  country  has  knowledge  of  any 
infraction  of  the  Convention  or  of  the  Regulations  committed  in  any  of  the 
stations  authorized  by  it,  it  shall  ascertain  the  facts  and  fix  the  responsibility. 

In  the  case  of  stations  on  shipboard,  if  the  operator  is  responsible  for  such 
infraction,  the  management  of  the  radio  service  shall  take  the  necessary  meas- 
ures, and,  if  the  necessity  should  arise,  withdraw  the  certificate.  If  it  is 
ascertained  that  the  infraction  is  the  result  of  the  condition  of  the  apparatus 
or  of  instructions  given  the  operator,  the  same  method  shall  be  pursued  with 
regard  to  the  license  issued  to  the  vessel. 

2.  In  cases  of  repeated  infractions  chargeable  to  the  same  vessel,  if  the  rep- 
resentations made  to  the  management  of  the  country  to  which  the  vessel  is 
subject  by  that  of  another  country  remain  without  effect,  the  latter  shall  be  at 
liberty,  after  giving  due  notice,  to  authorize  its  coastal  stations  not  to  accept 
communications  proceeding  from  the  vessel  at  fault.  In  case  of  disagreement 
between  the  managements  of  the  radio  service  of  two  countries,  the  question 
shall  be  submitted  to  arbitration  at  the  request  of  either  of  the  two  Govern- 
ments concerned.    The  procedure  is  indicated  in  Article  18*  of  the  Convention. 

*  Gives  rules  governing  arbitration. 
16 


242  APPENDICES. 

2.    HOURS   OF   SERVICE  OF   STATIONS. 

Article  XIII. 

(a)  Coastal  stations: 

1.  The  service  of  coastal  stations  shall,  as  far  as  possible,  be  constant,  day 
and  night,  vs^ithout  interruption. 

Certain  coastal  stations,  however,  may  have  a  service  of  limited  duration 
The  management  of  the  radio  service  of  each  country  shall  fix  the  hours  of 
service. 

2.  The  coastal  stations  whose  service  is  not  constant  shall  not  close  before 
having  transmitted  all  their  radiograms  to  the  vessels  which  are  within 
their  radius  of  action,  nor  before  having  received  from  such  vessels  all  the 
radiograms  of  which  notice  has  been  given.  This  provision  is  likewise  applica- 
ble when  vessels  signal  their  presence  before  the  actual  cessation  of  work. 

(b)  Stations  on  shipboard: 

3.  Stations  on  shipboard  shall  be  classed  under  three  categories: 

(1)  Stations  having  constant  service; 

(2)  Stations  having  a  service  of  limited  duration; 

(3)  Stations   having  no   fixed   working  hours. 

When  the  ship  is  under  way,  the  following  shipboard  stations  shall  have  an 
operator  constantly  listening  in;  1st,  Stations  of  the  first  category;  2nd,  Those 
of  the  second  category  during  the  hours  in  which  they  are  open  to  service. 
During  the  remaining  hours,  the  last  named  stations  shall  have  an  operator 
at  the  radio  instrument  listening  in  during  the  first  ten  minutes  of  each  hour. 
Stations  of  the  third  category  are  not  bound  to  perform  any  regular  service 
of  listening  in. 

It  shall  fall  to  the  Governments  issuing  the  licenses  specified  in  Article  IX 
to  fix  the  category  in  which  the  ship  shall  be  classed  as  regards  its  obligations 
in  the  matter  of  listening  in.  Mention  shall  be  made  of  such  classification 
in  the  license. 

3.    FORM    AND   posting   OF   RADIOGRAMS. 

Article  XIV. 

1.  Radiograms  shall  show,  as  the  first  word  of  the  preamble,  that  the  service 
is  "  radio." 

2.  In  the  transmission  of  radiograms  proceeding  from  a  ship  at  sea,  the  date 
and  hour  of  posting  at  the  shipboard  station  shall  be  stated  in  the  preamble. 

3.  Upon  forwarding  a  radiogram  over  the  telegraph  system,  the  coastal 
station  shall  show  thereon  as  the  office  of  origin,  the  name  of  the  ship  of  origin 
as  it  appears  in  the  list,  and  also  when  the  case  arises,  that  of  the  last  ship 
which  acted  as  intermediary.  These  data  shall  be  followed  by  the  name  of 
Che  coastal  station. 

Article  XV. 
The  address  of  radiograms  intended  for  ships  shall  be  as  complete  as  possible. 
It  shall  embrace  the  following: 

(a)  The  name  or  title  of  the  addressee,  with  additional  designations,  if  any; 

(b)  The  name  of  the  vessel  as  it  appears  in  the  first  column  of  the  list; 

(c)  The  name  of  the  coastal  station  as  it  appears  in  the  list. 


APPENDICES.  243 

The  name  of  the  ship,  however,  may  be  replaced,  at  the  sender's  risk,  by  the 
designation  of  the  route  to  be  followed  by  such  vessel,  as  determined  by  the 
names  of  the  ports  of  departure  and  destination  or  by  any  other  equivalent 
information. 

2.  In  the  address,  the  name  of  the  ship  as  it  appears  in  the  first  column  of 
the  list,  shaH,  in  all  cases  and  independently  of  its  length,  be  counted  as  one 
word. 

3.  Radiograms  framed  with  the  aid  of  the  International  Code  of  Signals 
shall  be  transmitted  to  their  destination  without  being  translated. 

4.    RATES. 

Article  XVI. 

1.  The  coastal  rate  and  the  shipboard  rate  shall  be  fixed  in  accordance  with 
the  tariff  per  word,  pure  and  simple,  on  the  basis  of  an  equitable  remuneration 
for  the  radio  work,  with  an  optional  minimum  rate  per  radiogram. 

The  coastal  rate  shall  not  exceed  60  centimes  (11.6  cents)  a  word,  and  the 
shipboard  rate  shall  not  exoeed  40  centimes  (7.7  cents)  a  word.  However, 
each  management  shall  be  at  liberty  to  authorize  coastal  and  shipboard  ratea 
higher  than  such  maxima  in  the  case  of  stations  of  ranges  exceeding  400 
nautical  miles,  or  of  stations  whose  work  is  exceptionally  difficult  owing  to 
physical  conditions  in  connection  with  the  installation  or  working  of  the 
same. 

The  optional  minimum  rate  per  radiogram  shall  not  be  higher  than  the 
coastal  rate  or  shipboard  rate  for  a  radiogram  of  ten  words. 

2.  In  the  case  of  radiograms  proceeding  from  or  destined  for  a  country  and 
exchanged  directly  with  the  coastal  stations  of  such  country,  the  rate  applicable 
to  the  transmission  over  the  telegraph  lines  shall  not,  on  the  average,  exceed 
the  inland  rate  of  such  country. 

Such  rate  shall  be  computed  per  word,  pure  and  simple,  with  an  optional 
minimum  rate  which  shall  not  exceed  the  rate  for  ten  words.  It  shall  be  stated 
in  francs  by  the  management  of  the  radio  service  of  the  country  to  which  the 
coastal  station  is  subject. 

In  the  case  of  countries  of  the  European  system,  with  the  exception  of 
Russia  and  Turkey,  there  shall  be  but  one  rate  for  the  territory  of  each 
country. 

Article  XVII. 

1.  "When  a  radiogram  proceeding  from  a  ship  and  intended  for  the  coast 
passes  through  one  or  two  shipboard  stations,  the  charges  shall  comprise, 
in  addition  to  the  rates  of  the  shipboard  station  of  origin,  the  coastal  station 
and  the  telegraph  lines,  the  shipboard  rate  of  each  of  the  ships  which  have 
participated  in  the  transmission. 

2.  The  sender  of  a  radiogram  proceeding  from  the  coast  and  intended  for 
a  ship  may  require  that  his  message  be  transmitted  by  way  of  one  or  two 
stations  on  shipboard;  he  shall  deposit  for  this  purpose  an  amount  equal  to  the 
radio  and  telegraph  rates,  and,  in  addition,  a  sum  to  be  fixed  by  the  office  of 
origin,  as  surety  for  the  payment  to  the  intermediary  shipboard  stations  of 
the  transit  rates  fixed  by  paragraph  1.  He  shall  further  pay,  at  his  option, 
either  the  rate  for  a  telegram  of  five  words  or  the  price  of  the  postage  on  a 


244  APPENDICES. 

letter  to  be  sent  by  the  coastal  station  to  the  ofl5ce  of  origin  giving  the  neces- 
sary Information  for  the  liquidation  of  the  amounts  deposited. 

The  radiogram  shall  then  be  accepted  at  the  sender's  risk;  it  shall  show 
before  the  address  the  prepaid  instruction,  to  wit:  "  X  retransmissions 
telegraph  "  or  "  X  retransmissions  letter "  according  to  whether  the  sender 
desired  the  information  necessary  for  the  liquidation  of  the  deposits  to  be 
furnished  by  telegraph  or  by  letter. 

3.  The  rate  for  radiograms  proceeding  from  a  ship  intended  for  another  ship, 
and  forwarded  through  one  or  two  intermediary  coastal  stations,  shall  com- 
prise: 

The  shipboard  rates  of  the  two  ships,  the  coastal  rate  of  the  coastal  station 
or  two  coastal  stations,  as  the  case  may  be,  and  the  telegraph  rate,  when  nec- 
essary, applicable  to  the  transmission  between  the  two  coastal  stations. 

4.  The  rate  for  radiograms  exchanged  between  ships  without  the  interven- 
tion of  a  coastal  station  shall  comprise  the  shipboard  rates  of  the  vessels  of 
origin  and  destination  together  with  the  shipboard  rates  of  the  intermediary 
stations. 

5.  The  coastal  and  shipboard  rates  accruing  to  the  stations  of  transit  shall 
be  the  same  as  those  fixed  for  such  stations  when  they  are  stations  of  origin 
or  destination.    In  no  case  shall  they  be  collected  more  than  once. 

6.  In  the  case  of  every  coastal  station  acting  as  intermediary,  the  rate 
to  be  collected  for  the  service  of  transit  shall  be  the  highest  coastal  rate  appli- 
cable to  direct  communication  with  the  two  ships  concerned. 

Article  XVIII. 
The  country  within  whose  territory  a  coastal  station  is  established  which 
serves  as  intermediary  for  the  exchange  of  radiograms  between  a  station  on 
board  ship  and  another  country  shall  be  considered,  so  far  as  the  application 
of  telegraph  rates  is  concerned,  as  the  country  of  origin  or  of  destination  of 
such  radiograms,  and  not  as  the  country  of  transit. 

5.   COLLECTION    OF   CHARGES. 

Article  XIX. 

The  total  charge  for  radiograms  shall  be  collected  of  the  sender  with 
the  exception  of: 

(1)  Charges  for  special  delivery  (Art.  LVIII,  Par.  1,  of  the  Telegraph  Reg- 
ulations);  (2)  Charges  applicable  to  inadmissable  combinations  or  alterations 
of  words  noted  by  the  oflBce  or  station  of  destination  (Art.  XIX,  par.  9  of  the 
Telegraph  Regulations)  such  charges  being  collected  of  the  addressee. 

Stations  on  shipboard  shall  to  that  end  have  the  necessary  tariffs.  They 
shall  be  at  liberty,  however,  to  obtain  information  from  coastal  stations  on  the 
subject  of  rates  for  radiograms  for  which  they  do  not  possess  all  the  necessary 
data. 

2.  The  counting  of  words  by  the  office  of  origin  shall  be  conclusive  in  the 
case  of  radiograms  intended  for  ships  and  that  of  the  shipboard  of  origin 
shall  be  conclusive  in  the  case  of  radiograms  proceeding  from  ships,  both  for 
purposes  of  transmission  and  of  the  international  accounts.  However,  when 
the  radiogram  is  worded  wholly  or  in  part,  either  in  one  of  the  languages  of 
the  country  of  destination,  in  the  case  of  radiograms  proceeding  from  ships,  or 
in  one  of  the  languages  of  the  country  to  which  the  ship  is  subject,  in  the  case 


APPENDICES.  245 

of  radiograms  intended  for  ships,  and  contains  combinations  or  alterations  of 
words  contrary  to  the  usage  of  such  language,  the  bureau  or  shipboard  station 
of  destination,  as  the  case  may  be,  shall  have  the  right  to  recover  from  the 
addressee  the  amount  of  charge  not  collected.  In  case  of  refusal  to  pay,  the 
radiogram  may  be  withheld. 

6.   TEANSMISSION  OF  BADIOGBAMS. 
(a)    signals  of  TRANSMISSION. 

Article  XX. 
The  signals  to  be  employed  are  those  of  the  Morse  International  Code. 

Article  XXI. 
Ships  in  distress  shall  use  the  following  signal: 

•  ••      ■■■■■1      ••• 

repeated  at  brief  intervals,  followed  by  the  necessary  particulars. 

As  soon  as  a  station  hears  the  signal  of  distress  it  shall  cease  all  correspon- 
dence and  not  resume  it  until  after  it  has  made  sure  that  the  correspondence 
to  which  the  call  for  assistance  has  given  rise  is  terminated. 

Stations  which  hear  a  signal  of  distress  shall  conform  to  the  instructions 
given  by  the  ship  making  such  signal  as  regards  the  order  of  the  messages  or 
their  cessation. 

In  case  the  call  letters  of  a  particular  station  are  added  at  the  end  of  the 
series  of  calls  for  assistance,  the  answer  to  the  call  shall  be  incumbent  upon 
that  station  alone  unless  such  station  fails  to  reply.  If  the  call  for  assistance 
does  not  specify  any  particular  station,  every  station  hearing  such  call  shall 
be  bound  to  answer  it. 


APPENDIX  D. 

[Public— No.  262.] 
[S.  7021.] 

An  Act  to  require  apparatus  and  operators  for  radio-communication  on 
certain  ocean  steamers. 

Be  it  enacted  hy  the  Senate  and  House  of  Representatives  of  the  United 
States  of  America  in  Congress  assembled,  That  from  and  after  the  first  day 
of  July,  nineteen  hundred  and  eleven,  it  shall  be  unlawful  for  any  ocean- 
going steamer  of  the  United  States,  or  of  any  foreign  counry,  carrying 
passengers  and  carrying  fifty  or  more  persons,  including  passengers  and 
crew,  to  leave  or  attempt  to  leave  any  port  of  the  United  States  unless  such 
steamer  shall  be  equipped  with  an  eflBcient  apparatus  for  radio-communica- 
tion, In  good  working  order,  in  charge  of  a  person  skilled  in  the  use  of  such 
apparatus,  which  apparatus  shall  be  capable  of  transmitting  and  receiving 
messages  over  a  distance  of  at  least  one  hundred  miles,  night  or  day: 
Provided,  That  the  provisions  of  this  Act  shall  not  apply  to  steamers  plying 
only  between  ports  less  than  two  hundred  miles  apart. 

Sec.  2.  That  for  the  purpose  of  this  Act  apparatus  for  radio-communi- 
cation shall  not  be  deemed  to  be  eflacient  unless  the  company  installing  it 


246  APPENDICES. 

shall  contract  in  writing  to  exchange,  and  shall,  in  fact,  exchange,  as  far  as 
may  be  physically  practicable,  to  be  determined  by  the  master  of  the  vessel, 
messages  with  shore  or  ship  stations  using  other  systems  of  radio-communi- 
cation. 

Sec.  3.  That  the  master  or  other  person  being  in  charge  of  any  such 
vessel  which  leaves  or  attempts  to  leave  any  port  of  the  United  States  in 
violation  of  any  of  the  provisions  of  this  Act  shall,  upon  conviction,  be  fined 
in  a  sum  not  more  than  five  thousand  dollars,  and  any  such  fine  shall  be  a 
lien  upon  such  vessel,  and  such  vessel  may  be  libeled  therefor  in  any  district 
court  of  the  United  States  within  the  jurisdiction  of  which  such  vessel  shall 
arrive  or  depart,  and  the  leaving  or  attempting  to  leave  each  and  every  port 
of  the  United  States  shall  constitute  a  separate  offense. 

Sec.  4.  That  the  Secretary  of  Commerce  and  Labor  shall  make  such 
regulations  as  may  be  necessary  to  secure  the  proper  execution  of  this  Act 
by  collectors  of  customs  and  other  officers  of  the  government. 

Approved,  June  24,  1910. 

[Public— No.  264.] 
[S.  6412J 

An  Act  to  regulate  radio  communication. 

Be  it  enacted  'by  the  Senate  and  House  of  Representatives  of  the  United  States 
of  America  in  Congress  assemhled,  That  a  person,  company  or  corporation 
within  the  jurisdiction  of  the  United  States  shall  not  use  or  operate  any  appa- 
ratus for  radio  communication  as  a  means  of  commercial  intercourse  among 
the  several  states,  or  with  foreign  nations,  or  upon  any  vessel  of  the  United 
States  engaged  in  interstate  or  foreign  commerce,  or  for  the  transmission  of 
radiograms  or  signals  the  effect  of  which  extends  beyond  the  jurisdiction  of  the 
State  or  Territory  in  which  the  same  are  made,  or  where  interference  would 
be  caused  thereby  with  the  receipt  of  messages  or  signals  from  beyond  the 
jurisdiction  of  the  said  State  or  Territory,  except  under  and  in  accordance 
with  a  license,  revocable  for  cause,  in  that  behalf  granted  by  the  Secretary  of 
Commerce  and  Labor  upon  application  therefor;  but  nothing  in  this  Act  shall 
be  construed  to  apply  to  the  transmission  and  exchange  of  radiograms  or  sij- 
nals  between  points  situated  in  the  same  State;  Provided,  That  the  effect 
thereof  shall  not  extend  beyond  the  jurisdiction  of  the  said  State  or  interfere 
with  the  reception  of  radiograms  or  signals  from  beyond  said  jurisdiction;  and 
a  license  shall  not  be  required  for  the  transmission  or  exchange  of  radiograms 
or  signals  by  or  on  behalf  of  the  Government  of  the  United  States,  but  every 
Government  station  on  land  or  sea  shall  have  special  call  letters  designated 
and  published  in  the  list  of  radio  stations  of  the  United  States  by  the  Depart- 
ment of  Commerce  and  Labor.  Any  person,  company,  or  corporation  that  shall 
use  or  operate  any  apparatus  for  radio  communication  in  violation  of  this 
section,  or  knowingly  aid  or  abet  another  person,  company,  or  corporation  In 
so  doing,  shall  be  deemed  guilty  of  a  misdemeanor,  and  on  conviction  thereof 
shall  be  punished  by  a  fine  not  exceeding  five  hundred  dollars,  and  the  appa- 
ratus or  device  so  unlawfully  used  and  operated  may  be  adjudged  forfeited  to 
the  United  States. 

Sec.  2.  That  every  such  license  shall  be  in  such  form  as  the  Secretary  of 
Commerce  and  Labor  shall  determine  and  shall  contain  the  restrictions,  pur- 
suant to  this  Act,  on  and  subject  to  which  the  license  is  granted;  that  every 
such  license  shall  be  issued  only  to  citizens  of  the  United  States  or  Porto 


APPENDICES.  247 

Rico  or  to  a  company  incorporated  under  tlie  laws  of  some  State  or  Terri- 
tory or  of  tlie  United  States  or  Porto  Rico,  and  shall  specify  the  ownership 
and  location  of  the  station  in  which  said  apparatus  shall  be  used  and  other 
particulars  for  its  identification  and  to  enable  its  range  to  be  estimated;  shall 
state  the  purpose  of  the  station,  and,  in  case  of  a  station  in  actual  operation 
at  the  date  of  passage  of  tliis  Act,  shall  contain  the  statement  that  satisfactory 
proof  has  been  furnished  that  it  was  actually  operating  on  the  above-men- 
tioned date;  shall  state  the  wave  length  or  the  wave  lengths  authorized  for  use 
by  the  station  for  the  prevention  of  interference  and  the  hours  for  which  the 
station  is  licensed  for  work;  and  shall  not  be  construed  to  authorize  the  use  of 
any  apparatus  for  radio  communication  in  any  other  station  than  that  speci- 
fied. Every  such  license  shall  be  subject  to  the  regulations  contained  herein, 
and  such  regulations  as  may  be  established  from  time  to  time  by  authority 
of  this  Act  or  subsequent  Acts  and  treaties  of  the  United  States.  Every  such 
license  shall  provide  that  the  President  of  the  United  States  in  time  of  war 
or  public  peril  or  disaster  may  cause  the  closing  of  any  station  for  radio-com- 
munication and  the  removal  therefrom  of  all  radio  apparatus,  or  may  authorize 
the  use  or  control  of  any  such  station  or  apparatus  by  any  department  of  the 
Government,  upon  just  compensation  to  the  owners. 

Sec.  3.  That  every  such  apparatus  shall  at  all  times  while  in  use  and  opera- 
tion as  aforesaid  be  in  charge  or  under  the  supervision  of  a  person  or  persons 
licensed  for  that  purpose  by  the  Secretary  of  Commerce  and  Labor.  Every 
person  so  licensed  who  in  the  operation  of  any  radio  apparatus  shall  fail  to 
observe  and  obey  regulations  contained  in  or  made  pursuant  to  this  Act  or 
subsequent  acts  or  treaties  of  the  United  States,  or  any  one  of  them,  or  who 
shall  fail  to  enforce  obedience  thereto  by  an  unlicensed  person  while  serving 
under  his  supervision,  in  addition  to  the  punishments  and  penalties  herein  pre- 
scribed, may  suffer  the  suspension  of  the  said  license  for  a  period  to  be  fixed  by 
the  Secretary  of  Commerce  and  Labor  not  exceeding  one  year.  It  shall  be  un- 
lawful to  employ  any  unlicensed  person  or  for  any  unlicensed  person  to  serve 
in  charge  or  in  supervision  of  the  use  and  operation  of  such  apparatus,  and  any 
person  violating  this  provision  shall  be  'guilty  of  a  misdemeanor,  and  on  convic- 
tion thereof  shall  be  punished  by  a  fine  of  not  more  than  one  hundred  dollars  or 
imprisonment  for  not  more  than  two  months,  or  both,  in  the  discretion  of  the 
court  for  each  and  every  such  offense:  Provided,  That  in  case  of  emergency 
the  Secretary  of  Commerce  and  Labor  may  authorize  a  collector  of  customs  to 
issue  a  temporary  permit,  in  lieu  of  a  license,  to  the  operator  on  a  vessel  sub- 
ject to  the  radio  ship  Act  of  June  twenty-fourth,  nineteen  hundred  and  ten. 

4.  That  for  the  purpose  of  preventing  or  minimizing  interference  with  com- 
munication between  stations  in  which  such  apparatus  is  operated,  to  facilitate 
radio  communication,  and  to  further  the  prompt  receipt  of  distress  signals, 
said  private  and  commercial  stations  shall  be  subject  to  the  regulations  of 
this  section.  These  regulations  shall  be  enforced  by  the  Secretary  of  Commerce 
and  Labor  through  the  collectors  of  customs  and  other  oflacers  of  the  Govern- 
ment as  other  regulations  herein  provide  for. 

The  Secretary  of  Commerce  and  Labor  may,  in  his  discretion,  waive  the  pro- 
visions of  any  or  all  of  these  regulations  when  no  interference  of  the  character 
above  mentioned  can  ensue. 

The  Secretary  of  Commerce  and  Labor  may  grant  special  temporary  licenses 
to  stations  actually  engaged  in  conducting  experiments  for  the  development 
of  the  science  of  radio  communication,  or  the  apparatus  pertaining  thereto, 
to  carry  on  special  tests,  using  any  amount  of  power  or  any  wave  lengths,  at 


248  APPENDICES. 

such  hours  and  under  such  conditions  as  will  Insure  the  least  interference  with 
the  sending  or  receipt  of  commercial  or  Government  radiograms,  of  distress 
signals  and  radiograms,  or  with  the  work  of  other  stations. 

In  these  regulations  the  naval  and  military  stations  shall  be  understood  to  be 
stations  on  land. 

Reqitlations. 

normal  wave  length. 
First.  Every  station  shall  be  required  to  designate  a  certain  definite  wave 
length  as  the  normal  sending  and  receiving  wave  length  of  the  station.  This 
wave  length  shall  not  exceed  six  hundred  meters  or  it  shall  exceed  one 
thousand  six  hundred  meters.  Every  coastal  station  open  to  general  public 
service  shall  at  all  times  be  ready  to  receive  messages  of  such  wave  lengths 
as  are  required  by  the  Berlin  convention.  Every  ship  station,  except  as  herein- 
after provided,  and  every  coast  station  open  to  general  public  service  shall  be 
prepared  to  use  two  sending  wave  lengths,  one  of  three  hundred  meters  and 
one  of  six  hundred  meters,  as  required  by  the  International  convention  in 
force:  Provided,  That  the  Secretary  of  Commerce  and  Labor  may,  in  his  dis- 
cretion, change  the  limit  of  wave  length  reservation  made  by  regulations  first 
and  second  to  accord  with  any  international  agreement  to  which  the  United 
States  is  a  party. 

OTHEB  WAVE  LENGTHS. 

Second.  In  addition  to  the  normal  sending  wave  length  all  stations,  except 
as  provided  hereinafter  in  these  regulations,  may  use  other  sending  wave 
lengths:  Provided,  That  they  do  not  exceed  six  hundred  meters  or  that  they 
do  exceed  one  thousand  six  hundred  meters;  Provided  further,  That  the 
character  of  the  waves  emitted  conforms  to  the  requirements  of  regulations 
third  and  fourth  following. 

USE   OF   A    "  PUBE  WAVE." 

Third.  At  all  stations  if  the  sending  apparatus,  to  be  referred  to  hereinafter 
as  the  "  transmitter,"  is  of  such  a  character  that  the  energy  is  radiated  in 
two  or  more  wave  lengths,  more  or  less  sharply  defined,  as  indicated  by  a  sen- 
sitive wave  meter,  the  energy  in  no  one  of  the  lesser  waves  shall  exceed  ten 
per  centum  of  that  in  the  greatest. 

USE  OF  A  "  SHARP  WAVE." 

Fourth.  At  all  stations  the  logarithmic  decrement  per  complete  oscillation 
In  the  wave  trains  emitted  by  the  transmitter  shall  not  exceed  two-tenths  except 
when  sending  distress  signals  or  signals  and  messages  relating  thereto. 

USE   OF   "  STANDARD   DISTRESS   WAVE." 

Fifth.  Every  station  on  shipboard  shall  be  prepared  to  send  distress  calla 
on  the  normal  wave  length  designated  by  the  international  convention  in  force, 
except  on  vessels  of  small  tonnage  unable  to  have  plants  insuring  that  wave 
length. 

SIGNAL  OF  DISTRESS. 

Sixth.  The  distress  call  used  shall  be  the  international  signal  of  distress 


APPENDICES.  249 

USE   OF   "  BROAD  INTERFERING  WAVE  "   FOR  DISTRESS    SIGNALS. 

Seventh.  When  sending  distress  signals,  the  transmitter  of  a  station  on  ship- 
board may  be  tuned  in  such  a  manner  as  to  create  a  maximum  of  interference 
with  a  maximum  of  radiation. 

DISTANCE  REQUIREMENT  FOR  DISTRESS   SIGNALS. 

Eighth.  Every  station  on  shipboard,  wherever  practicable,  shall  be  prepared 
to  send  distress  signals  of  the  character  specified  in  regulations  fifth  and  sixth 
with  suflBcient  power  to  enable  them  to  be  received  by  day  over  sea  a  distance 
of  one  hundred  nautical  miles  by  a  shipboard  station  equipped  with  apparatus 
for  both  sending  and  receiving  equal  in  all  essential  particulars  to  that  of  the 
station  first  mentioned. 

"  RIGHT  OF  WAY  "  FOR  DISTRESS  SIGNALS. 

Ninth.  All  stations  are  required  to  give  absolute  priority  to  signals  and 
radiograms  relating  to  ships  in  distress;  to  cease  all  sending  on  hearing  a 
distress  signal;  and,  except  when  engaged  in  answering  or  aiding  the  ship  in 
distress,  to  refrain  from  sending  until  all  signals  and  radiograms  relating 
thereto  are  completed. 

REDUCED   POWER   FOR   SHIPS    NEAR   A   GOVERNMENT   STATION. 

Tenth.  No  station  on  shipboard,  when  within  fifteen  nautical  miles  of  a 
naval  or  military  station,  shall  use  a  transformer  input  exceeding  one  kilowatt, 
nor,  when  within  five  nautical  miles  of  such  a  station,  a  transformer  input 
exceeding  one-half  kilowatt,  except  for  sending  signals  of  distress,  or  signals 
or  radiograms  relating  thereto. 

INTERCOMMUNICATION. 

Eleventh.  Each  shore  station  open  to  general  public  service  between  the 
coast  and  vessels  at  sea  shall  be  bound  to  exchange  radiograms  with  any  simi- 
lar shore  station  and  with  any  ship  station  without  distinction  of  the  radio 
systems  adopted  by  such  stations,  respectively,  and  each  station  on  shipboard 
shall  be  bound  to  exchange  radiograms  with  any  other  station  on  shipboard 
without  distinction  of  the  radio  systems  adopted  by  each  station,  respectively. 

It  shall  be  the  duty  of  each  such  shore  station,  during  the  hours  it  is  in  opera- 
tion, to  listen  in  at  intervals  of  not  less  than  fifteen  minutes  and  for  a  period 
not  less  than  two  minutes,  with  the  receiver  tuned  to  receive  messages  of  three 
hundred  meter  wave  lengths. 

DIVISION  OF  TIME. 

Twelfth.  At  important  seaports  and  at  all  other  places  where  naval  or  mili- 
tary and  private  or  commercial  shore  stations  operate  in  such  close  proximity 
that  interference  with  the  work  of  naval  and  military  stations  can  not  be 
avoided  by  the  enforcement  of  the  regulations  contained  in  the  foregoing  regu- 
lations concerning  wave  lengths  and  character  of  signals  emitted,  such  private 
or  commercial  shore  stations  as  do  interfere  with  the  reception  of  signals  by 
the  naval  and  military  stations  concerned  shall  not  use  their  transmitters 
during  the  first  fifteen  minutes  of  each  hour,  local  standard  time.  The  Sec- 
retary of  Commerce  and  Labor  may,  on  the  recommendation  of  the  depart- 
ment concerned,  designate  the  station  or  stations  which  may  be  required  to 
observe  this  division  of  time. 


250  APPENDICES. 

GOVERNMENT  STATIONS   TO  OBSERVE   DIVISION   OF  TIME. 

Thirteenth.  The  naval  or  military  stations  for  which  the  above-mentioned 
division  of  time  may  be  established  shall  transmit  signals  or  radiograms  only 
during  the  first  fifteen  minutes  of  each  hour,  local  standard  time,  except  in 
case  of  signals  or  radiograms  relating  to  vessels  in  distress,  as  hereinbefore 
provided. 

USE  OF  UNNECESSARY  POWER. 

Fourteenth.  In  all  circumstances,  except  in  case  of  signals  or  radiograms 
relating  to  vessels  in  distress,  all  stations  shall  use  the  minimum  amount  of 
energy  necessary  to  carry  out  any  communication   desired. 

GENERAL  RESTRICTIONS  ON  PRIVATE  STATIONS. 

Fifteenth.  No  private  or  commercial  station  not  engaged  in  the  transaction 
of  bona  fide  commercial  business  by  radio  communication  or  in  experimenta- 
tion in  connection  with  the  development  and  manufacture  of  radio  apparatus 
for  commercial  purposes  shall  use  a  transmitting  wave  length  exceeding  two 
hundred  meters,  or  a  transformer  input  exceeding  one  kilowatt,  except  by 
special  authority  of  the  Secretary  of  Commerce  and  Labor  contained  in  the 
license  of  the  station:  Provided,  That  the  owner  or  operator  of  a  station  of  the 
character  mentioned  in  this  regulation  shall  not  be  liable  for  a  violation  of  the 
requirements  of  the  third  or  fourth  regulations  to  the  penalties  of  one  hundred 
dollars  or  twenty-five  dollars,  respectively,  provided  in  this  section  unless  the 
person  maintaining  or  operating  such  station  shall  have  been  notified  in  writ- 
ing that  the  said  transmitter  has  been  found,  upon  tests  conducted  by  the 
Government,  to  be  so  adjusted  as  to  violate  the  said  third  and  fourth  regula- 
tions, and  opportunity  has  been  given  to  said  owner  or  operator  to  adjust  said 
transmitter  in  conformity  with  said  regulations. 

SPECIAL   RESTRICTIONS    IN    THE    VICINITIES    OF   GOVERNMENT    STATIONS. 

Sixteenth.  No  station  of  the  character  mentioned  in  regulation  fifteenth 
situated  within  five  nautical  miles  of  a  naval  or  military  station  shall  use  a 
transmitting  wave  length  exceeding  two  hundred  meters  or  a  transformer 
Input  exceeding  one-half  kilowatt. 

SHIP  STATIONS  TO  COMMUNICATE  WITH  NEAREST  SHORE  STATIONS. 

Seventeenth.  In  general,  the  shipboard  stations  shall  transmit  their  radio- 
grams to  the  nearest  shore  station.  A  sender  on  board  a  vessel  shall,  however, 
have  the  right  to  designate  the  shore  station  through  which  he  desires  to 
have  his  radiograms  transmitted.  If  this  can  not  be  done,  the  wishes  of  the 
sender  are  to  be  complied  with  only  if  the  transmission  can  be  effected  without 
interfering  with  the  service  of  other  stations. 

LIMITATIONS  FOR  FUTURE  INSTALLATIONS  IN   VICINITIES  OF  GOVERNMENT  STATIONS. 

Eighteenth.  No  station  on  shore  not  in  actual  operation  at  the  date  of  the 
passage  of  this  Act  shall  be  licensed  for  the  transaction  of  commercial  busi- 
ness by  radio  communication  within  fifteen  nautical  miles  of  the  following 
naval  or  military  stations,  to  wit:  Arlington,  Virginia;  Key  West,  Florida; 
San  Juan,  Porto  Rico;  North  Head  and  Tatoosh  Island,  Washington;  San 
Diego,  California;  and  those  established  or  which  may  be  established  in  Alaska 
and  in  the  Canal  Zone;  and  the  head  of  the  department  having  control  of  such 
Government  stations  shall,  so  far  as  is  consistent  with  the  transaction  of  gov- 
ernmental business,  arrange  for  the  transmission  and  receipt  of  commercial 
radiograms  under  the  provisions  of  the  Berlin  convention  of  nineteen  hundred 


APPENDICES.  251 

and  six  and  future  international  conventions  or  treaties  to  which  tlie  United 
States  may  be  a  party,  at  each  of  the  stations  above  referred  to,  and  shall  fix 
the  rates  therefor,  subject  to  control  of  such  rates  by  Congress.  At  such  sta- 
tions and  wherever  and  whenever  shore  stations  open  for  general  public  busi- 
ness between  the  coast  and  vessels  at  sea  under  the  provisions  of  the  Berlin  con- 
vention of  nineteen  hundred  and  six  and  future  international  conventions  and 
treaties  to  which  the  United  States  may  be  a  party  shall  not  be  so  established  as 
to  insure  a  constant  service  day  and  night  without  interruption,  and  in  all 
localities  wherever  or  whenever  such  service  shall  not  be  maintained  by  a  com- 
mercial shore  station  within  one  hundred  nautical  miles  of  a  naval  radio  sta- 
tion, the  Secretary  of  the  Navy  shall,  so  far  as  is  consistent  with  the  transac- 
tion of  governmental  business,  open  naval  radio  stations  to  the  general  public 
business  described  above,  and  shall  fix  rates  for  such  service,  subject  to  control 
of  such  rates  by  Congress.  The  receipts  from  such  radiograms  shall  be  covered 
Into  the  Treasury  as  miscellaneous  receipts. 

SECBECY  OF  MESSAGES. 

Nineteenth.  No  person  or  persons  engaged  in  or  having  knowledge  of  the 
operation  of  any  station  or  stations,  shall  divulge  or  publish  the  contents  of 
any  messages  transmitted  or  received  by  such  station,  except  to  the  person 
or  persons  to  whom  the  same  may  be  directed,  or  their  authorized  agent,  or 
to  another  station  employed  to  forward  such  message  to  its  destination,  unless 
legally  required  so  to  do  by  the  court  of  competent  jurisdiction  or  other  com- 
petent authority.  Any  person  guilty  of  divulging  or  publishing  any  message, 
except  as  herein  provided,  shall,  on  conviction  thereof,  be  punishable  by  a  fine 
of  not  more  than  two  hundred  and  fifty  dollars  or  imprisonment  for  a  period 
of  not  exceeding  three  months,  or  both  fine  and  imprisonment,  in  the  discretion 
of  the  court. 

PENALTIES. 

For  violation  of  any  of  these  regulations,  subject  to  which  a  license  under 
sections  one  and  two  of  this  Act  may  be  issued,  the  owner  of  the  apparatus 
shall  be  liable  to  a  penalty  of  one  hundred  dollars,  which  may  be  reduced  or 
remitted  by  the  Secretary  of  Commerce  and  Labor,  and  for  repeated  violations 
of  any  of  such  regulations,  the  license  may  be  revoked. 

For  violation  of  any  of  these  regulations,  except  as  provided  in  regulation 
nineteenth,  subject  to  which  a  license  under  section  three  of  this  Act  may  be 
issued,  the  operator  shall  be  subject  to  a  penalty  of  twenty-five  dollars  which 
may  be  reduced  or  remitted  by  the  Secretary  of  Commerce  and  Labor,  and  for 
repeated  violations  of  any  such  regulations,  the  license  shall  be  suspended  or 
revoked. 

Sec.  5.  That  every  license  granted  under  the  provisions  of  this  Act  for  the 
operation  or  use  of  apparatus  for  radio  communication  shall  prescribe  that  the 
operator  thereof  shall  not  wilfully  or  maliciously  interfere  with  any  other 
radio  communication.  Such  Interference  shall  be  deemed  a  misdemeanor,  and 
upon  conviction  thereof  the  owner  or  operator,  or  both,  shall  be  punishable 
by  a  fine  of  not  to  exceed  five  hundred  dollars  or  imprisonment  for  not  to  exceed 
one  year,  or  both. 

Sec.  6.  That  the  expression  "  radio  communication  "  as  used  in  this  Act 
means  any  system  of  electrical  communication  by  telegraphy  or  telephony  with- 
out the  aid  of  any  wire  connecting  the  points  from  and  at  which  the  radio- 
grams, signals,  or  other  communications  are  sent  or  received. 


252  APPENDICES. 

Sec.  7.  That  a  person,  company,  or  corporation  within  the  jurisdiction  of 
the  United  States  shall  not  knowingly  utter  or  transmit,  or  cause  to  be  uttered 
or  transmitted,  any  false  or  fraudulent  distress  signal  or  call  or  false  or 
fraudulent  signal,  call,  or  other  radiogram  of  any  kind.  The  penalty  for  so 
uttering  or  transmitting  a  false  or  fraudulent  distress  signal  or  call  shall  be 
a  fine  of  not  more  than  two  thousand  five  hundred  dollars  or  imprisonment 
for  not  more  than  five  years,  or  both,  in  the  discretion  of  the  court,  for 
each  and  every  such  offense,  and  the  penalty  for  so  uttering  or  transmitting, 
or  causing  to  be  uttered  or  transmitted,  any  other  false  or  fraudulent  signal, 
call,  or  other  radiogram  shall  be  a  fine  of  not  more  than  one  thousand  dollars 
or  imprisonment  for  not  more  than  two  years,  or  both,  in  the  discretion  of  the 
court,  for  each  and  every  such  offense. 

Sec.  8.  That  a  person,  company,  or  corporation  shall  not  use  or  operate 
any  apparatus  for  radio  communication  on  a  foreign  ship  in  territorial  waters 
of  the  United  States  otherwise  than  in  accordance  with  the  provisions  of  sec- 
tions four  and  seven  of  this  Act  and  so  much  of  section  five  as  imposes  a 
penalty  for  interference.  Save  as  aforesaid,  nothing  in  this  Act  shall  apply 
to  apparatus  for  radio  communication  on  any  foreign  ship. 

Sec.  9.  That  the  trial  of  any  offense  under  this  Act  shall  be  in  the  district 
in  which  it  is  committed,  or  if  the  offense  is  committed  upon  the  high  seas  or 
out  of  the  jurisdiction  of  any  particular  State  or  district  the  trial  shall  be  in 
the  district  where  the  offender  may  be  found  or  into  which  he  shall  be  first 
brought. 

Sec.  10.  That  this  Act  shall  not  apply  to  the  Philippine  Islands. 

Sec.  11.  That  this  Act  shall  take  effect  and  be  in  force  on  and  after  four 
months  from  its  passage. 

Approved,  August  13,  1912. 


APPENDIX  E. 
Routine  fob  the  Upkeep  of  Coastal  Radio  Stations. 

DAILY. 

1.  Wipe  off  all  instruments  carefully,  using  chamois  skin  or  soft  cloth  to 
polish  slate  panels  and  hard  rubber  parts. 

2.  Examine  contacts  of  receiving  circuits  and  remove  all  dirt  or  corrosion  if 
any  collected. 

3.  If  crystal  detector  is  used,  clean  same  by  using  bisulphide  of  carbon,  or 
soap  and  water,  using  a  soft  bristle  brush.  This  will  increase  the  sensitive- 
ness and  prolong  the  life  of  the  crystals. 

4.  If  quenched  gap  is  used,  clean  and  readjust  the  gaps.  If  rotating  gap  is 
used,  examine  both  stationary  electrodes  and  studs  to  ascertain  if  they  have 
burned  away  leaving  the  gap  too  wide.  If  open  gap  is  used  and  compressed 
air  is  used  for  ventilation  of  gap,  blow  water  out  of  air  lines;  examine  and 
readjust  the  spark  terminals  to  prevent  the  gap  from  becoming  too  wide. 

5.  Inspect  the  lubricating  system  of  cylinders  and  bearings  whether  gravity 
feed,  ring  feed  or  forced  feed  and  make  sure  the  feed  pipes  and  oil  grooves  are 
not  clogged. 

6.  If  oil  engine  is  used,  fill  cylinder  cup  and  lubricate  governor. 


APPENDICES.  253 

7.  In  winter  tend  heating  apparatus  carefully  to  prevent  freezing  of  water 
In  cylinder,  pipes,  etc.,  and  keep  oil  fluid  if  necessary. 

8.  Clear  spark,  using  wave  meter  to  ascertain  when  tone  is  clear. 

1.  Rub  down  slate  panels  and  instrument  cases.  Examine  all  contacts  on 
circuit  breakers,  fuses  and  switches.    Vaseline  moving  contacts  lightly. 

2.  When  compressed  air  is  available,  blow  out  fields  and  armatures  of  motor- 
generators  and  motors,  otherwise  clean  anyway  possible.  Clean  commutators 
and  collector  rings  and  adjust  brushes.  Examine  all  connections  for  fields, 
armature  and  automatic  or  hand  starter.  Take  H.  W.  A.  readings  using  full 
power  to  determine  if  any  loss  in  radiation,  and  correct  same  if  found  to  exist. 

3.  Pump  up  air  condensers  if  installed. 

4.  Dismount  Leyden  jar  battery  and  clean  jars.  Pay  special  attention  to 
cleaning  glass  above  coating,  inside  and  out,  rack  and  contacts,  if  necessary. 
Clean  thoroughly  and  set  up  all  contacts  of  transmitter.  Exposed  leads  of 
transmitter  and  inductances  may  be  polished  and  then  lacquered  to  retain  their 
polish. 

5.  "Wipe  off  the  exterior  of  transformer  and  induction  coils.  Examine  all 
rheostats  and  reactance  regulators  carefully. 

6.  Clean  all  gauze  strainers  and  lubricate  the  working  parts  of  all  valves 
in  pipe  lines  and  operate  the  same. 

7.  Clean  and  dress  down  key  contacts.    Renew  if  necessary. 

8.  Vaseline  lightly  the  contacts  of  aerial  and  lightning  switches. 

MONTHLY. 

1.  Make  Cadmium  and  Hydrometer  tests  of  storage  battery  if  installed. 
Pour  out  the  solution  of  any  cell  found  to  have  a  specific  gravity  of  less  than 
1.140.  Examine  the  plates  and  set  up  all  contacts  while  the  cell  is  empty. 
Then  fill  with  new  solution. 

Follow  carefully  special  instructions  for  care  and  operation  of  storage  bat- 
teries. 

2.  Clean  oil  injection  nozzles. 

3.  Examine  the  bearings  of  all  generators  and  motors  and  refit  same  before 
armature  strikes  the  pole  pieces. 

4.  Pack  stuffing  boxes  of  valves  in  pipe  lines. 

5.  Make  notes  on  recording  instruments,  for  comparison  to  detect  any  devi- 
ation that  may  exist. 

SEMI-ANNUAXLY. 

1.  Change  oil  in  motors  and  generators.  Also  in  dash  pot  of  automatic 
starter  if  fitted.  (This  should  be  changed  monthly  in  high  speed  machines 
over  2500  R.  P.  M.) 

2.  Refit  and  line  bearings  of  motors  and  generators  if  necessary.  If  oil 
engine  is  used  dismount  and  clean  port  openings,  combustion  spaces,  jackets 
of  cylinders  and  renew  gaskets  if  necesary. 

3.  Dismount  and  seat,  check  and  reducing  valves.  Renew  Asbestos  packing 
of  oil  pump. 

4.  Overhaul  all  rigging,  oil  blocks  and  tar  standing  parts.  Renew  halliards 
when  necessary. 

Do  any  other  work  required  by  peculiarities  of  station. 


354  APPENDICES. 

APPENDIX  F. 
Resuscitation  from  Apparent  Death  from  Electric  Shock. 

BY   AUGUSTIN   H.   GOEXET,   M.  D, 

The  urgent  necessity  for  prompt  and  persistent  efforts  at  resuscitation  of 
victims  of  accidental  shocks  by  electricity  is  very  well  emphasized  by  the 
successful  results  in  the  instances  recorded.  In  order  that  the  task  may  not 
be  undertaken  in  a  half-hearted  manner,  it  must  be  appreciated  that  accidental 
shocks  seldom  result  in  absolute  death  unless  the  victim  is  left  unaided  too 
long,  or  efforts  at  resuscitation  are  stopped  too  early. 

In  the  majority  of  instances  the  shock  is  only  sufficient  to  suspend  anima- 
tion temporarily,  owing  to  the  momentary  and  imperfect  contact  of  the  con- 
ductors, and  also  on  account  of  the  resistance  of  the  body  submitted  to  the 
influence  of  the  current.  It  must  be  appreciated  also  that  the  body  under  the 
conditions  of  accidental  shocks  seldom  receives  the  full  force  of  the  current 
in  the  circuit,  but  only  a  shunt  current,  which  may  represent  a  very  insig- 
nificant part  of  the  whole. 

When  an  accident  occurs,  the  following  rules  should  be  promptly  executed 
with  care  and  deliberation: 

1.  Remove  the  body  at  once  from  the  circuit  by  breaking  contact  with  the 
conductors.  This  may  be  accomplished  by  using  a  dry  stick  of  wood,  which 
is  a  nonconductor,  to  roll  the  body  over  to  one  side,  or  to  brush  aside  a  wire, 
if  that  is  conveying  the  current.  When  a  stick  is  not  at  hand,  any  dry  piece 
of  clothing  may  be  utilized  to  protect  the  hand  in  seizing  the  body  of  the 
victim,  unless  rubber  gloves  are  convenient.  If  the  body  is  in  contact  with 
the  earth,  the  coat  tails  of  the  victim,  or  any  loose  or  detached  piece  of  cloth- 
ing may  be  seized  with  impunity  to  draw  it  away  from  the  conductor.  When 
this  has  been  accomplished  observe  rule  2.  The  object  to  be  attained  is  to 
make  the  subject  breathe,  and  if  this  can  be  accomplished  and  continued  he 
can  be  saved. 

2.  Turn  the  body  upon  the  back,  loosen  the  collar  and  clothing  about  the 
neck,  roll  up  a  coat  and  place  it  under  the  shoulders,  so  as  to  throw  the  head 
back,  and  then  make  efforts  to  establish  respiration  (in  other  words,  make 
him  breathe),  just  as  would  be  done  in  case  of  drowning.  To  accomplish  this, 
kneel  at  the  subject's  head,  facing  him,  and  seizing  both  arms  draw  them 
forcibly  to  their  full  length  over  the  head,  so  as  to  bring  them  almost  to- 
gether above  it,  and  hold  them  there  for  two  or  three  seconds  only.  (This  is 
to  expand  the  chest  and  favor  the  entrance  of  air  into  the  lungs.)  Then 
carry  the  arms  down  to  the  sides  and  front  of  the  chest,  firmly  compressing 
the  chest  walls,  and  expel  the  air  from  the  lungs.  Repeat  this  maneuver  at 
least  sixteen  times  per  minute.  .  These  efforts  should  be  continued  unremit- 
tingly for  at  least  an  hour,  or  until  natural  respiration  is  established. 

3.  At  the  same  time  that  this  is  being  done,  some  one  should  grasp  the 
tongue  of  the  subject  with  a  handkerchief  or  piece  of  cloth  to  prevent  it  slip- 
ping, and  draw  it  forcibly  out  when  the  arms  are  extended  above  the  head 
and  allow  it  to  recede  when  the  chest  is  compressed.  This  maneuver  should 
likewise  be  repeated  at  least  sixteen  times  per  minute.  This  serves  the  double 
purpose  of  freeing  the  throat  so  as  to  permit  air  to  enter  the  lungs,  and  also 
by  exciting  a  reflex  irritation  from  forcible  contact  of  the  under  part  of  the 
tongue  against  the  lower  teeth,  frequently  stimulates  an  involuntary  effort  at 
respiration.  To  secure  the  tongue  if  the  teeth  are  clenched,  force  the  jaw 
apart  with  a  stick,  a  piece  of  wood,  or  the  handle  of  a  pocket  knife. 


APPENDICES.  255 

4.  The  dashing  of  cold  water  into  the  face  will  sometimes  produce  a  gasp 
and  start  breathing,  which  should  then  be  continued  as  directed  above.  If 
this  is  not  successful  the  spine  may  be  rubbed  vigorously  with  a  piece  of  ice. 
Alternate  applications  of  heat  and  cold  over  the  region  of  the  heart  will 
accomplish  the  same  object  in  some  instances.  It  is  both  useless  and  unwise 
to  attempt  to  administer  stimulants  to  the  victim  in  the  usual  manner  by 
pouring  them  down  his  throat. 

While  the  above  directions  are  being  carried  out,  a  physician  should  be 
summoned,  who,  upon  his  arrival,  can  best  put  into  practice  rules  5,  6.  and  7, 
In  addition  to  the  foregoing,  should  it  be  necessary. 

For  the  Physician  Summoned. 

5.  Forcible  stretching  of  the  sphincter  muscle  controlling  the  lower  bowel 
excites  powerful  reflex  irritation  and  stimulates  a  gasp  (inspiration)  fre- 
quently when  other  measures  have  failed.  For  this  purpose,  the  subject  should 
be  turned  on  the  side,  the  middle  and  index  fingers  inserted  into  the  rectum, 
and  the  muscle  suddenly  and  forcibly  drawn  backward  toward  the  spine.  Or, 
if  it  is  desirable  to  continue  efforts  at  artificial  respiration  at  the  same  time, 
the  knees  should  be  drawn  up  and  the  thumb  inserted  for  the  same  purpose, 
the  subject  retaining  the  position  on  the  back. 

6.  Rythmical  traction  of  the  tongue  is  sometimes  effectual  in  establishing 
respiration  when  other  measures  have  failed.  The  tongue  is  seized  and  drawn 
out  quickly  and  forcibly  to  the  limit,  then  it  is  permitted  to  recede.  This  is 
to  be  repeated  16  times  per  minute. 

7.  Oxygen  gas,  which  may  be  readily  obtained  at  a  drug  store  in  cities  or 
large  towns,  is  a  powerful  stimulant  to  the  heart  if  it  can  be  made  to  enter 
the  lungs.  A  cone  may  be  improvised  from  a  piece  of  stiff  paper  and  attached 
to  the  tube  leading  from  the  tank,  and  placed  over  the  mouth  and  nose  while 
the  gas  is  turned  on  during  the  efforts  at  artificial  respiration. 


256 


APPENDICES. 


Alpena,  Mich. 

Annapolis,  Md. 

Astoria,  Oregon. 

Avalon,  Calif. 

Balboa,  C.  Z. 

Beaufort,  N.  C. 

Boston  (Filene  Building.) 

Boston,  Mass. 

Buffalo,  N.  Y. 

Burrwood,  La. 

Calumet,  Mich. 

Cape  Cod,  Mass. 

Cape  May,  N.  J. 

Cavite,  P.  I. 

Charleston,  S.  C. 

Cleveland,  Ohio. 

Colon,  C.  Z. 

Cordova,  Alaska. 

Darien,  C.  Z. 

Detroit,  Mich. 

Diamond  Shoals  Lightship. 

Duluth,  Minn. 

Dutch  Harbor,  Alaska. 

Bast  San  Pedro,  Calif. 

Eureka,  Calif. 

Ensenada,  P.  R. 

Farallon  Islands,  Calif. 

Fire  Island,  N.  Y. 

Fire  Island  Lightship. 

Frankfort,  Mich. 

Frying  Pan  Shoals  Lightship. 

Galveston,  Texas. 

Great  Lakes,  111. 

Guam,  M.  I. 

Guantanamo  Bay,  Cuba. 

Heald  Bank  Lightship,  Galveston. 

Heeia  Point,  T.  H. 

Hillcrest,  Calif. 

Inglewood,  Calif. 

Juneau,  Alaska. 

Jupiter,  Fla. 

Kahuku,  T.  H. 

Kaunakakai,  T.  H. 

Kawaihae,  T.  H. 

Ketchikan,  Alaska. 

Key  West,  Fla. 

Kodiak,  Alaska. 

Lahaina,  T.  H. 

Lents,  Oregon. 


APPENDIX  G. 

NAVAL  RADIO  STATIONS. 

January  1,  1918. 

Lihue,  T.  H. 


Ludington,  Mich. 

Manistique,  Mich. 

Manitowoc,  Wis. 

Marshall,  Calif. 

Marshfield,  Calif. 

Miami,  Fla. 

Milwaukee,  Wis. 

Mobile,  Ala. 

Nantucket  Shoals  Lightship. 

Navassa  Island. 

New  Orleans,  La. 

Newport,  R.  I. 

New  York,  N.  Y. 

Norfolk,  Va. 

North  Head,  Wash. 

Olongapo,  P.  I. 

Pearl  Harbor,  T.  H. 

Peking,  China. 

Pensacola,  Fla. 

Philadelphia,  Pa. 

Point  Arguello,  Calif. 

Point  Isabel,  Texas. 

Port  Arthur,  Texas. 

Portland,  Maine. 

Portsmouth,  N.  H. 

Puget  Sound,  Wash. 

San  Diego,  Calif. 

San  Francisco,  Calif. 

San  Francisco  (Beach.) 

San  Francisco  (Hobart  Bldg.) 

San  Juan,  P.  R. 

Sayville,  L.  I. 

Seattle,  Wash. 

Seward,  Alaska. 

Siasconsett,  Mass. 

Sitka,  Alaska. 

South  Wellfleet,  Mass. 

St.  Augustine,  Fla. 

St.  George,  Pribilof  Islands. 

St.  Paul,  Pribilof  Islands. 

St.  Thomas,  Virgin  Islands. 

Tampa,  Fla. 

Tatoosh,  Wash. 

Tutuila,  Samoa. 

Tuckerton,  N.  J. 

Virginia  Beach,  Va. 

Washington  (Arlington.) 

Wahiawa,  T.  H. 


UNIVEKSITY  OF  CALIFORNIA  LIBRARY, 

BERKELEY 

THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 

STAMPED  BELOW 

Books  not  returned  on  time  are  subject  to  a  fine  of 
50c  per  volume  after  the  third  day  overdue,  increasing 
to  $1.00  per  volume  after  the  sixth  day.     Books  not  in 
demand  may  be  renewed  if  application   is  made  before 
expiration   of  loan  period. 

: _ .— 

^       MAH  11  t92t 

NOV  131982.    , 

1    .  APB  14.  m\ 

fiECCiR.  JAM  19  '83 

; 

fW^Y  8f^  tg?? 

mi71§22 

QCT  ii2  r^^K- 

WAR  X^  ^^^^ 

20m-ll,'20 

iC I 05b85 

,,y,,C,  BERKELEY  LIBRARIES 


CDbl3flE7ai 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


KINGS 

ooK  Store 

16    MARKET    ST 


WMm 


